diff --git a/Source/Core/Core/IOS/ES/Formats.cpp b/Source/Core/Core/IOS/ES/Formats.cpp
index 4f4fb7a43e..d8a5af7a10 100644
--- a/Source/Core/Core/IOS/ES/Formats.cpp
+++ b/Source/Core/Core/IOS/ES/Formats.cpp
@@ -16,6 +16,7 @@
 #include <utility>
 #include <vector>
 
+#include <fmt/format.h>
 #include <mbedtls/sha1.h>
 
 #include "Common/Assert.h"
@@ -320,7 +321,7 @@ std::string TMDReader::GetGameID() const
   if (all_printable)
     return std::string(game_id, sizeof(game_id));
 
-  return StringFromFormat("%016" PRIx64, GetTitleId());
+  return fmt::format("{:016x}", GetTitleId());
 }
 
 std::string TMDReader::GetGameTDBID() const
@@ -334,7 +335,7 @@ std::string TMDReader::GetGameTDBID() const
   if (all_printable)
     return std::string(begin, end);
 
-  return StringFromFormat("%016" PRIx64, GetTitleId());
+  return fmt::format("{:016x}", GetTitleId());
 }
 
 u16 TMDReader::GetNumContents() const
@@ -547,7 +548,7 @@ struct SharedContentMap::Entry
   std::array<u8, 20> sha1;
 };
 
-static const std::string CONTENT_MAP_PATH = "/shared1/content.map";
+constexpr char CONTENT_MAP_PATH[] = "/shared1/content.map";
 SharedContentMap::SharedContentMap(std::shared_ptr<HLE::FS::FileSystem> fs) : m_fs{fs}
 {
   static_assert(sizeof(Entry) == 28, "SharedContentMap::Entry has the wrong size");
@@ -572,7 +573,7 @@ SharedContentMap::GetFilenameFromSHA1(const std::array<u8, 20>& sha1) const
     return {};
 
   const std::string id_string(it->id.begin(), it->id.end());
-  return StringFromFormat("/shared1/%s.app", id_string.c_str());
+  return fmt::format("/shared1/{}.app", id_string);
 }
 
 std::vector<std::array<u8, 20>> SharedContentMap::GetHashes() const
@@ -591,14 +592,14 @@ std::string SharedContentMap::AddSharedContent(const std::array<u8, 20>& sha1)
   if (filename)
     return *filename;
 
-  const std::string id = StringFromFormat("%08x", m_last_id);
+  const std::string id = fmt::format("{:08x}", m_last_id);
   Entry entry;
   std::copy(id.cbegin(), id.cend(), entry.id.begin());
   entry.sha1 = sha1;
   m_entries.push_back(entry);
 
   WriteEntries();
-  filename = StringFromFormat("/shared1/%s.app", id.c_str());
+  filename = fmt::format("/shared1/{}.app", id);
   m_last_id++;
   return *filename;
 }
@@ -640,7 +641,7 @@ static std::pair<u32, u64> ReadUidSysEntry(const HLE::FS::FileHandle& file)
   return {Common::swap32(uid), Common::swap64(title_id)};
 }
 
-static const std::string UID_MAP_PATH = "/sys/uid.sys";
+constexpr char UID_MAP_PATH[] = "/sys/uid.sys";
 UIDSys::UIDSys(std::shared_ptr<HLE::FS::FileSystem> fs) : m_fs{fs}
 {
   if (const auto file = fs->OpenFile(PID_KERNEL, PID_KERNEL, UID_MAP_PATH, HLE::FS::Mode::Read))
diff --git a/Source/Core/Core/IOS/ES/NandUtils.cpp b/Source/Core/Core/IOS/ES/NandUtils.cpp
index a0bbcad55f..5e98ed618b 100644
--- a/Source/Core/Core/IOS/ES/NandUtils.cpp
+++ b/Source/Core/Core/IOS/ES/NandUtils.cpp
@@ -12,6 +12,8 @@
 #include <unordered_set>
 #include <vector>
 
+#include <fmt/format.h>
+
 #include "Common/CommonTypes.h"
 #include "Common/Logging/Log.h"
 #include "Common/NandPaths.h"
@@ -86,8 +88,8 @@ static std::vector<u64> GetTitlesInTitleOrImport(FS::FileSystem* fs, const std::
     if (!IsValidPartOfTitleID(title_type))
       continue;
 
-    const auto title_entries =
-        fs->ReadDirectory(PID_KERNEL, PID_KERNEL, titles_dir + '/' + title_type);
+    const std::string title_dir = fmt::format("{}/{}", titles_dir, title_type);
+    const auto title_entries = fs->ReadDirectory(PID_KERNEL, PID_KERNEL, title_dir);
     if (!title_entries)
       continue;
 
@@ -96,8 +98,10 @@ static std::vector<u64> GetTitlesInTitleOrImport(FS::FileSystem* fs, const std::
       if (!IsValidPartOfTitleID(title_identifier))
         continue;
       if (!fs->ReadDirectory(PID_KERNEL, PID_KERNEL,
-                             titles_dir + '/' + title_type + '/' + title_identifier))
+                             fmt::format("{}/{}", title_dir, title_identifier)))
+      {
         continue;
+      }
 
       const u32 type = std::stoul(title_type, nullptr, 16);
       const u32 identifier = std::stoul(title_identifier, nullptr, 16);
@@ -150,7 +154,8 @@ std::vector<u64> ES::GetTitlesWithTickets() const
     for (const std::string& file_name : *sub_entries)
     {
       const std::string name_without_ext = file_name.substr(0, 8);
-      if (fs->ReadDirectory(PID_KERNEL, PID_KERNEL, "/ticket/" + title_type + '/' + file_name) ||
+      if (fs->ReadDirectory(PID_KERNEL, PID_KERNEL,
+                            fmt::format("/ticket/{}/{}", title_type, file_name)) ||
           !IsValidPartOfTitleID(name_without_ext) || name_without_ext + ".tik" != file_name)
       {
         continue;
@@ -299,13 +304,13 @@ bool ES::FinishImport(const IOS::ES::TMDReader& tmd)
   // Remove everything not listed in the TMD.
   std::unordered_set<std::string> expected_entries = {"title.tmd"};
   for (const auto& content_info : tmd.GetContents())
-    expected_entries.insert(StringFromFormat("%08x.app", content_info.id));
+    expected_entries.insert(fmt::format("{:08x}.app", content_info.id));
   const auto entries = fs->ReadDirectory(PID_KERNEL, PID_KERNEL, import_content_dir);
   if (!entries)
     return false;
   for (const std::string& name : *entries)
   {
-    const std::string absolute_path = import_content_dir + '/' + name;
+    const std::string absolute_path = fmt::format("{}/{}", import_content_dir, name);
     // There should not be any directory in there. Remove it.
     if (fs->ReadDirectory(PID_KERNEL, PID_KERNEL, absolute_path))
       fs->Delete(PID_KERNEL, PID_KERNEL, absolute_path);
@@ -333,7 +338,8 @@ bool ES::WriteImportTMD(const IOS::ES::TMDReader& tmd)
       return false;
   }
 
-  const std::string dest = Common::GetImportTitlePath(tmd.GetTitleId()) + "/content/title.tmd";
+  const std::string dest =
+      fmt::format("{}/content/title.tmd", Common::GetImportTitlePath(tmd.GetTitleId()));
   return fs->Rename(PID_KERNEL, PID_KERNEL, tmd_path, dest) == FS::ResultCode::Success;
 }
 
@@ -365,7 +371,7 @@ std::string ES::GetContentPath(const u64 title_id, const IOS::ES::Content& conte
 {
   if (content.IsShared())
     return content_map.GetFilenameFromSHA1(content.sha1).value_or("");
-  return Common::GetTitleContentPath(title_id) + StringFromFormat("/%08x.app", content.id);
+  return fmt::format("{}/{:08x}.app", Common::GetTitleContentPath(title_id), content.id);
 }
 
 std::string ES::GetContentPath(const u64 title_id, const IOS::ES::Content& content) const
diff --git a/Source/Core/Core/IOS/ES/TitleManagement.cpp b/Source/Core/Core/IOS/ES/TitleManagement.cpp
index 5a5a077157..d415e44f2a 100644
--- a/Source/Core/Core/IOS/ES/TitleManagement.cpp
+++ b/Source/Core/Core/IOS/ES/TitleManagement.cpp
@@ -10,12 +10,12 @@
 #include <utility>
 #include <vector>
 
+#include <fmt/format.h>
 #include <mbedtls/sha1.h>
 
 #include "Common/Align.h"
 #include "Common/Logging/Log.h"
 #include "Common/NandPaths.h"
-#include "Common/StringUtil.h"
 #include "Core/CommonTitles.h"
 #include "Core/HW/Memmap.h"
 #include "Core/IOS/ES/Formats.h"
@@ -350,7 +350,7 @@ static bool CheckIfContentHashMatches(const std::vector<u8>& content, const IOS:
 
 static std::string GetImportContentPath(u64 title_id, u32 content_id)
 {
-  return Common::GetImportTitlePath(title_id) + StringFromFormat("/content/%08x.app", content_id);
+  return fmt::format("{}/content/{:08x}.app", Common::GetImportTitlePath(title_id), content_id);
 }
 
 ReturnCode ES::ImportContentEnd(Context& context, u32 content_fd)
@@ -438,8 +438,7 @@ static bool HasAllRequiredContents(IOS::HLE::Kernel& ios, const IOS::ES::TMDRead
 
     // Note: the import hasn't been finalised yet, so the whole title directory
     // is still in /import, not /title.
-    const std::string path =
-        Common::GetImportTitlePath(title_id) + StringFromFormat("/content/%08x.app", content.id);
+    const std::string path = GetImportContentPath(title_id, content.id);
     return ios.GetFS()->GetMetadata(PID_KERNEL, PID_KERNEL, path).Succeeded();
   });
 }
@@ -567,7 +566,7 @@ ReturnCode ES::DeleteTicket(const u8* ticket_view)
 
   // Delete the ticket directory if it is now empty.
   const std::string ticket_parent_dir =
-      StringFromFormat("/ticket/%08x", static_cast<u32>(title_id >> 32));
+      fmt::format("/ticket/{:08x}", static_cast<u32>(title_id >> 32));
   const auto ticket_parent_dir_entries =
       fs->ReadDirectory(PID_KERNEL, PID_KERNEL, ticket_parent_dir);
   if (ticket_parent_dir_entries && ticket_parent_dir_entries->empty())
@@ -625,9 +624,9 @@ ReturnCode ES::DeleteContent(u64 title_id, u32 content_id) const
   if (!tmd.FindContentById(content_id, &content))
     return ES_EINVAL;
 
-  return FS::ConvertResult(m_ios.GetFS()->Delete(PID_KERNEL, PID_KERNEL,
-                                                 Common::GetTitleContentPath(title_id) +
-                                                     StringFromFormat("/%08x.app", content_id)));
+  const std::string path =
+      fmt::format("{}/{:08x}.app", Common::GetTitleContentPath(title_id), content_id);
+  return FS::ConvertResult(m_ios.GetFS()->Delete(PID_KERNEL, PID_KERNEL, path));
 }
 
 IPCCommandResult ES::DeleteContent(const IOCtlVRequest& request)
diff --git a/Source/Core/Core/IOS/FS/FileSystemProxy.cpp b/Source/Core/Core/IOS/FS/FileSystemProxy.cpp
index d844963ea2..a044d2b9d0 100644
--- a/Source/Core/Core/IOS/FS/FileSystemProxy.cpp
+++ b/Source/Core/Core/IOS/FS/FileSystemProxy.cpp
@@ -6,8 +6,10 @@
 
 #include <algorithm>
 #include <cstring>
+#include <string_view>
+
+#include <fmt/format.h>
 
-#include "Common/Assert.h"
 #include "Common/ChunkFile.h"
 #include "Common/StringUtil.h"
 #include "Common/Swap.h"
@@ -45,16 +47,19 @@ void FS::DoState(PointerWrap& p)
   p.Do(m_dirty_cache);
 }
 
-static void LogResult(const std::string& command, ResultCode code)
+template <typename... Args>
+static void LogResult(ResultCode code, std::string_view format, Args&&... args)
 {
+  const std::string command = fmt::format(format, std::forward<Args>(args)...);
   GENERIC_LOG(LogTypes::IOS_FS, (code == ResultCode::Success ? LogTypes::LINFO : LogTypes::LERROR),
               "%s: result %d", command.c_str(), ConvertResult(code));
 }
 
-template <typename T>
-static void LogResult(const std::string& command, const Result<T>& result)
+template <typename T, typename... Args>
+static void LogResult(const Result<T>& result, std::string_view format, Args&&... args)
 {
-  LogResult(command, result.Succeeded() ? ResultCode::Success : result.Error());
+  const auto result_code = result.Succeeded() ? ResultCode::Success : result.Error();
+  LogResult(result_code, format, std::forward<Args>(args)...);
 }
 
 enum class FileLookupMode
@@ -108,7 +113,7 @@ IPCCommandResult FS::Open(const OpenRequest& request)
 
   auto backend_fd = m_ios.GetFS()->OpenFile(request.uid, request.gid, request.path,
                                             static_cast<Mode>(request.flags & 3));
-  LogResult(StringFromFormat("OpenFile(%s)", request.path.c_str()), backend_fd);
+  LogResult(backend_fd, "OpenFile({})", request.path);
   if (!backend_fd)
     return GetFSReply(ConvertResult(backend_fd.Error()), ticks);
 
@@ -132,7 +137,7 @@ IPCCommandResult FS::Close(u32 fd)
       ticks += SUPERBLOCK_WRITE_TICKS;
 
     const ResultCode result = m_ios.GetFS()->Close(m_fd_map[fd].fs_fd);
-    LogResult(StringFromFormat("Close(%s)", m_fd_map[fd].name.data()), result);
+    LogResult(result, "Close({})", m_fd_map[fd].name.data());
     m_fd_map.erase(fd);
     if (result != ResultCode::Success)
       return GetFSReply(ConvertResult(result));
@@ -227,9 +232,7 @@ IPCCommandResult FS::Read(const ReadWriteRequest& request)
 
   const Result<u32> result = m_ios.GetFS()->ReadBytesFromFile(
       handle.fs_fd, Memory::GetPointer(request.buffer), request.size);
-  LogResult(
-      StringFromFormat("Read(%s, 0x%08x, %u)", handle.name.data(), request.buffer, request.size),
-      result);
+  LogResult(result, "Read({}, 0x{:08x}, {})", handle.name.data(), request.buffer, request.size);
   if (!result)
     return GetFSReply(ConvertResult(result.Error()));
 
@@ -247,9 +250,7 @@ IPCCommandResult FS::Write(const ReadWriteRequest& request)
 
   const Result<u32> result = m_ios.GetFS()->WriteBytesToFile(
       handle.fs_fd, Memory::GetPointer(request.buffer), request.size);
-  LogResult(
-      StringFromFormat("Write(%s, 0x%08x, %u)", handle.name.data(), request.buffer, request.size),
-      result);
+  LogResult(result, "Write({}, 0x{:08x}, {})", handle.name.data(), request.buffer, request.size);
   if (!result)
     return GetFSReply(ConvertResult(result.Error()));
 
@@ -264,9 +265,7 @@ IPCCommandResult FS::Seek(const SeekRequest& request)
 
   const Result<u32> result =
       m_ios.GetFS()->SeekFile(handle.fs_fd, request.offset, IOS::HLE::FS::SeekMode(request.mode));
-  LogResult(
-      StringFromFormat("Seek(%s, 0x%08x, %u)", handle.name.data(), request.offset, request.mode),
-      result);
+  LogResult(result, "Seek({}, 0x{:08x}, {})", handle.name.data(), request.offset, request.mode);
   if (!result)
     return GetFSReply(ConvertResult(result.Error()));
   return GetFSReply(*result);
@@ -378,7 +377,7 @@ IPCCommandResult FS::GetStats(const Handle& handle, const IOCtlRequest& request)
     return GetFSReply(ConvertResult(ResultCode::Invalid));
 
   const Result<NandStats> stats = m_ios.GetFS()->GetNandStats();
-  LogResult("GetNandStats", stats);
+  LogResult(stats, "GetNandStats");
   if (!stats)
     return GetDefaultReply(ConvertResult(stats.Error()));
 
@@ -402,7 +401,7 @@ IPCCommandResult FS::CreateDirectory(const Handle& handle, const IOCtlRequest& r
 
   const ResultCode result = m_ios.GetFS()->CreateDirectory(handle.uid, handle.gid, params->path,
                                                            params->attribute, params->modes);
-  LogResult(StringFromFormat("CreateDirectory(%s)", params->path), result);
+  LogResult(result, "CreateDirectory({})", params->path);
   return GetReplyForSuperblockOperation(result);
 }
 
@@ -438,7 +437,7 @@ IPCCommandResult FS::ReadDirectory(const Handle& handle, const IOCtlVRequest& re
   const std::string directory = Memory::GetString(request.in_vectors[0].address, 64);
   const Result<std::vector<std::string>> list =
       m_ios.GetFS()->ReadDirectory(handle.uid, handle.gid, directory);
-  LogResult(StringFromFormat("ReadDirectory(%s)", directory.c_str()), list);
+  LogResult(list, "ReadDirectory({})", directory);
   if (!list)
     return GetFSReply(ConvertResult(list.Error()));
 
@@ -468,7 +467,7 @@ IPCCommandResult FS::SetAttribute(const Handle& handle, const IOCtlRequest& requ
 
   const ResultCode result = m_ios.GetFS()->SetMetadata(
       handle.uid, params->path, params->uid, params->gid, params->attribute, params->modes);
-  LogResult(StringFromFormat("SetMetadata(%s)", params->path), result);
+  LogResult(result, "SetMetadata({})", params->path);
   return GetReplyForSuperblockOperation(result);
 }
 
@@ -480,7 +479,7 @@ IPCCommandResult FS::GetAttribute(const Handle& handle, const IOCtlRequest& requ
   const std::string path = Memory::GetString(request.buffer_in, 64);
   const u64 ticks = EstimateFileLookupTicks(path, FileLookupMode::Split);
   const Result<Metadata> metadata = m_ios.GetFS()->GetMetadata(handle.uid, handle.gid, path);
-  LogResult(StringFromFormat("GetMetadata(%s)", path.c_str()), metadata);
+  LogResult(metadata, "GetMetadata({})", path);
   if (!metadata)
     return GetFSReply(ConvertResult(metadata.Error()), ticks);
 
@@ -503,7 +502,7 @@ IPCCommandResult FS::DeleteFile(const Handle& handle, const IOCtlRequest& reques
 
   const std::string path = Memory::GetString(request.buffer_in, 64);
   const ResultCode result = m_ios.GetFS()->Delete(handle.uid, handle.gid, path);
-  LogResult(StringFromFormat("Delete(%s)", path.c_str()), result);
+  LogResult(result, "Delete({})", path);
   return GetReplyForSuperblockOperation(result);
 }
 
@@ -515,7 +514,7 @@ IPCCommandResult FS::RenameFile(const Handle& handle, const IOCtlRequest& reques
   const std::string old_path = Memory::GetString(request.buffer_in, 64);
   const std::string new_path = Memory::GetString(request.buffer_in + 64, 64);
   const ResultCode result = m_ios.GetFS()->Rename(handle.uid, handle.gid, old_path, new_path);
-  LogResult(StringFromFormat("Rename(%s, %s)", old_path.c_str(), new_path.c_str()), result);
+  LogResult(result, "Rename({}, {})", old_path, new_path);
   return GetReplyForSuperblockOperation(result);
 }
 
@@ -527,7 +526,7 @@ IPCCommandResult FS::CreateFile(const Handle& handle, const IOCtlRequest& reques
 
   const ResultCode result = m_ios.GetFS()->CreateFile(handle.uid, handle.gid, params->path,
                                                       params->attribute, params->modes);
-  LogResult(StringFromFormat("CreateFile(%s)", params->path), result);
+  LogResult(result, "CreateFile({})", params->path);
   return GetReplyForSuperblockOperation(result);
 }
 
@@ -548,7 +547,7 @@ IPCCommandResult FS::GetFileStats(const Handle& handle, const IOCtlRequest& requ
     return GetFSReply(ConvertResult(ResultCode::Invalid));
 
   const Result<FileStatus> status = m_ios.GetFS()->GetFileStatus(handle.fs_fd);
-  LogResult(StringFromFormat("GetFileStatus(%s)", handle.name.data()), status);
+  LogResult(status, "GetFileStatus({})", handle.name.data());
   if (!status)
     return GetDefaultReply(ConvertResult(status.Error()));
 
@@ -569,7 +568,7 @@ IPCCommandResult FS::GetUsage(const Handle& handle, const IOCtlVRequest& request
 
   const std::string directory = Memory::GetString(request.in_vectors[0].address, 64);
   const Result<DirectoryStats> stats = m_ios.GetFS()->GetDirectoryStats(directory);
-  LogResult(StringFromFormat("GetDirectoryStats(%s)", directory.c_str()), stats);
+  LogResult(stats, "GetDirectoryStats({})", directory);
   if (!stats)
     return GetFSReply(ConvertResult(stats.Error()));
 
diff --git a/Source/Core/Core/IOS/IOSC.cpp b/Source/Core/Core/IOS/IOSC.cpp
index c530109341..94159e1ce7 100644
--- a/Source/Core/Core/IOS/IOSC.cpp
+++ b/Source/Core/Core/IOS/IOSC.cpp
@@ -13,6 +13,7 @@
 #include <utility>
 #include <vector>
 
+#include <fmt/format.h>
 #include <mbedtls/md.h>
 #include <mbedtls/rsa.h>
 #include <mbedtls/sha1.h>
@@ -24,7 +25,6 @@
 #include "Common/File.h"
 #include "Common/FileUtil.h"
 #include "Common/ScopeGuard.h"
-#include "Common/StringUtil.h"
 #include "Common/Swap.h"
 #include "Core/IOS/Device.h"
 #include "Core/IOS/ES/Formats.h"
@@ -430,8 +430,8 @@ static CertECC MakeBlankEccCert(const std::string& issuer, const std::string& na
 
 CertECC IOSC::GetDeviceCertificate() const
 {
-  const std::string name = StringFromFormat("NG%08x", GetDeviceId());
-  auto cert = MakeBlankEccCert(StringFromFormat("Root-CA%08x-MS%08x", m_ca_id, m_ms_id), name,
+  const std::string name = fmt::format("NG{:08x}", GetDeviceId());
+  auto cert = MakeBlankEccCert(fmt::format("Root-CA{:08x}-MS{:08x}", m_ca_id, m_ms_id), name,
                                m_key_entries[HANDLE_CONSOLE_KEY].data.data(), m_console_key_id);
   cert.signature.sig = m_console_signature;
   return cert;
@@ -448,8 +448,8 @@ void IOSC::Sign(u8* sig_out, u8* ap_cert_out, u64 title_id, const u8* data, u32
   // ap_priv[0] &= 1;
 
   const std::string signer =
-      StringFromFormat("Root-CA%08x-MS%08x-NG%08x", m_ca_id, m_ms_id, GetDeviceId());
-  const std::string name = StringFromFormat("AP%016" PRIx64, title_id);
+      fmt::format("Root-CA{:08x}-MS{:08x}-NG{:08x}", m_ca_id, m_ms_id, GetDeviceId());
+  const std::string name = fmt::format("AP{:016x}", title_id);
   CertECC cert = MakeBlankEccCert(signer, name, ap_priv.data(), 0);
   // Sign the AP cert.
   const size_t skip = offsetof(CertECC, signature.issuer);
diff --git a/Source/Core/Core/IOS/Network/IP/Top.cpp b/Source/Core/Core/IOS/Network/IP/Top.cpp
index 2dddb53e54..303329254c 100644
--- a/Source/Core/Core/IOS/Network/IP/Top.cpp
+++ b/Source/Core/Core/IOS/Network/IP/Top.cpp
@@ -18,6 +18,8 @@
 #include <poll.h>
 #endif
 
+#include <fmt/format.h>
+
 #include "Common/Assert.h"
 #include "Common/CommonTypes.h"
 #include "Common/Logging/Log.h"
@@ -697,9 +699,9 @@ IPCCommandResult NetIPTop::HandleGetHostByNameRequest(const IOCtlRequest& reques
 
   for (int i = 0; remoteHost->h_addr_list[i]; ++i)
   {
-    u32 ip = Common::swap32(*(u32*)(remoteHost->h_addr_list[i]));
-    std::string ip_s =
-        StringFromFormat("%i.%i.%i.%i", ip >> 24, (ip >> 16) & 0xff, (ip >> 8) & 0xff, ip & 0xff);
+    const u32 ip = Common::swap32(*(u32*)(remoteHost->h_addr_list[i]));
+    const std::string ip_s =
+        fmt::format("{}.{}.{}.{}", ip >> 24, (ip >> 16) & 0xff, (ip >> 8) & 0xff, ip & 0xff);
     DEBUG_LOG(IOS_NET, "addr%i:%s", i, ip_s.c_str());
   }
 
diff --git a/Source/Core/Core/IOS/USB/Bluetooth/BTEmu.cpp b/Source/Core/Core/IOS/USB/Bluetooth/BTEmu.cpp
index ffb1d18c13..6737e41a76 100644
--- a/Source/Core/Core/IOS/USB/Bluetooth/BTEmu.cpp
+++ b/Source/Core/Core/IOS/USB/Bluetooth/BTEmu.cpp
@@ -5,11 +5,12 @@
 #include "Core/IOS/USB/Bluetooth/BTEmu.h"
 
 #include <algorithm>
-#include <cstdint>
 #include <cstring>
 #include <memory>
 #include <string>
 
+#include <fmt/format.h>
+
 #include "Common/Assert.h"
 #include "Common/Logging/Log.h"
 #include "Common/MsgHandler.h"
@@ -21,7 +22,6 @@
 #include "Core/HW/Memmap.h"
 #include "Core/HW/SystemTimers.h"
 #include "Core/HW/Wiimote.h"
-#include "Core/Host.h"
 #include "Core/IOS/Device.h"
 #include "Core/IOS/IOS.h"
 #include "Core/SysConf.h"
@@ -1781,7 +1781,7 @@ void BluetoothEmu::DisplayDisconnectMessage(const int wiimote_number, const int
   // mean
   // and display things like "Wii Remote %i disconnected due to inactivity!" etc.
   Core::DisplayMessage(
-      StringFromFormat("Wii Remote %i disconnected by emulated software", wiimote_number), 3000);
+      fmt::format("Wii Remote {} disconnected by emulated software", wiimote_number), 3000);
 }
 }  // namespace Device
 }  // namespace IOS::HLE
diff --git a/Source/Core/Core/IOS/USB/Common.cpp b/Source/Core/Core/IOS/USB/Common.cpp
index a37a4982e6..166ba9fff4 100644
--- a/Source/Core/Core/IOS/USB/Common.cpp
+++ b/Source/Core/Core/IOS/USB/Common.cpp
@@ -6,9 +6,10 @@
 
 #include <algorithm>
 
+#include <fmt/format.h>
+
 #include "Common/Assert.h"
 #include "Common/CommonTypes.h"
-#include "Common/StringUtil.h"
 #include "Common/Swap.h"
 #include "Core/HW/Memmap.h"
 
@@ -89,6 +90,6 @@ void EndpointDescriptor::Swap()
 
 std::string Device::GetErrorName(const int error_code) const
 {
-  return StringFromFormat("unknown error %d", error_code);
+  return fmt::format("unknown error {}", error_code);
 }
 }  // namespace IOS::HLE::USB
diff --git a/Source/Core/Core/IOS/WFS/WFSI.cpp b/Source/Core/Core/IOS/WFS/WFSI.cpp
index 0f98bf357f..3ef730bd86 100644
--- a/Source/Core/Core/IOS/WFS/WFSI.cpp
+++ b/Source/Core/Core/IOS/WFS/WFSI.cpp
@@ -11,6 +11,8 @@
 #include <utility>
 #include <vector>
 
+#include <fmt/format.h>
+
 #include "Common/CommonTypes.h"
 #include "Common/File.h"
 #include "Common/FileUtil.h"
@@ -25,13 +27,13 @@ namespace
 {
 std::string TitleIdStr(u64 tid)
 {
-  return StringFromFormat("%c%c%c%c", static_cast<char>(tid >> 24), static_cast<char>(tid >> 16),
-                          static_cast<char>(tid >> 8), static_cast<char>(tid));
+  return fmt::format("{}{}{}{}", static_cast<char>(tid >> 24), static_cast<char>(tid >> 16),
+                     static_cast<char>(tid >> 8), static_cast<char>(tid));
 }
 
 std::string GroupIdStr(u16 gid)
 {
-  return StringFromFormat("%c%c", gid >> 8, gid & 0xFF);
+  return fmt::format("{}{}", static_cast<char>(gid >> 8), static_cast<char>(gid & 0xFF));
 }
 }  // namespace
 
@@ -119,9 +121,8 @@ void WFSI::SetImportTitleIdAndGroupId(u64 tid, u16 gid)
 
 void WFSI::FinalizePatchInstall()
 {
-  const std::string current_title_dir =
-      StringFromFormat("/vol/%s/title/%s/%s", m_device_name.c_str(), m_current_group_id_str.c_str(),
-                       m_current_title_id_str.c_str());
+  const std::string current_title_dir = fmt::format("/vol/{}/title/{}/{}", m_device_name,
+                                                    m_current_group_id_str, m_current_title_id_str);
   const std::string patch_dir = current_title_dir + "/_patch";
   File::CopyDir(WFS::NativePath(patch_dir), WFS::NativePath(current_title_dir), true);
 }
@@ -145,9 +146,8 @@ IPCCommandResult WFSI::IOCtl(const IOCtlRequest& request)
 
     if (m_patch_type == PatchType::PATCH_TYPE_2)
     {
-      const std::string content_dir =
-          StringFromFormat("/vol/%s/title/%s/%s/content", m_device_name.c_str(),
-                           m_current_group_id_str.c_str(), m_current_title_id_str.c_str());
+      const std::string content_dir = fmt::format("/vol/{}/title/{}/{}/content", m_device_name,
+                                                  m_current_group_id_str, m_current_title_id_str);
 
       File::Rename(WFS::NativePath(content_dir + "/default.dol"),
                    WFS::NativePath(content_dir + "/_default.dol"));
@@ -185,7 +185,7 @@ IPCCommandResult WFSI::IOCtl(const IOCtlRequest& request)
   }
 
   case IOCTL_WFSI_PREPARE_PROFILE:
-    m_base_extract_path = StringFromFormat("/vol/%s/tmp/", m_device_name.c_str());
+    m_base_extract_path = fmt::format("/vol/{}/tmp/", m_device_name);
     [[fallthrough]];
 
   case IOCTL_WFSI_PREPARE_CONTENT:
@@ -274,14 +274,13 @@ IPCCommandResult WFSI::IOCtl(const IOCtlRequest& request)
     {
       // Delete content's default.dol
       const std::string title_content_dir =
-          StringFromFormat("/vol/%s/title/%s/%s/content/", m_device_name.c_str(),
-                           m_current_group_id_str.c_str(), m_current_title_id_str.c_str());
+          fmt::format("/vol/{}/title/{}/{}/content/", m_device_name, m_current_group_id_str,
+                      m_current_title_id_str);
       File::Delete(WFS::NativePath(title_content_dir + "default.dol"));
 
       // Copy content's _default.dol to patch's directory
-      const std::string patch_dir =
-          StringFromFormat("/vol/%s/title/%s/%s/_patch/", m_device_name.c_str(),
-                           m_current_group_id_str.c_str(), m_current_title_id_str.c_str());
+      const std::string patch_dir = fmt::format("/vol/{}/title/{}/{}/_patch/", m_device_name,
+                                                m_current_group_id_str, m_current_title_id_str);
       const std::string patch_content_dir = patch_dir + "content/";
       File::CreateDir(WFS::NativePath(patch_dir));
       File::CreateDir(WFS::NativePath(patch_content_dir));
@@ -293,28 +292,24 @@ IPCCommandResult WFSI::IOCtl(const IOCtlRequest& request)
     }
     case PATCH_TYPE_1:
     {
-      std::string patch_dir =
-          StringFromFormat("/vol/%s/title/%s/%s/_patch", m_device_name.c_str(),
-                           m_current_group_id_str.c_str(), m_current_title_id_str.c_str());
+      const std::string patch_dir = fmt::format("/vol/{}/title/{}/{}/_patch", m_device_name,
+                                                m_current_group_id_str, m_current_title_id_str);
       File::DeleteDirRecursively(WFS::NativePath(patch_dir));
 
-      tmd_path = StringFromFormat("/vol/%s/title/%s/%s/meta/%016" PRIx64 ".tmd",
-                                  m_device_name.c_str(), m_current_group_id_str.c_str(),
-                                  m_current_title_id_str.c_str(), m_import_title_id);
+      tmd_path = fmt::format("/vol/{}/title/{}/{}/meta/{:016x}.tmd", m_device_name,
+                             m_current_group_id_str, m_current_title_id_str, m_import_title_id);
       break;
     }
     case NOT_A_PATCH:
     {
-      std::string title_install_dir = StringFromFormat("/vol/%s/_install/%s", m_device_name.c_str(),
-                                                       m_import_title_id_str.c_str());
-      std::string title_final_dir =
-          StringFromFormat("/vol/%s/title/%s/%s", m_device_name.c_str(),
-                           m_import_group_id_str.c_str(), m_import_title_id_str.c_str());
+      const std::string title_install_dir =
+          fmt::format("/vol/{}/_install/{}", m_device_name, m_import_title_id_str);
+      const std::string title_final_dir = fmt::format("/vol/{}/title/{}/{}", m_device_name,
+                                                      m_import_group_id_str, m_import_title_id_str);
       File::Rename(WFS::NativePath(title_install_dir), WFS::NativePath(title_final_dir));
 
-      tmd_path = StringFromFormat("/vol/%s/title/%s/%s/meta/%016" PRIx64 ".tmd",
-                                  m_device_name.c_str(), m_import_group_id_str.c_str(),
-                                  m_import_title_id_str.c_str(), m_import_title_id);
+      tmd_path = fmt::format("/vol/{}/title/{}/{}/meta/{:016x}.tmd", m_device_name,
+                             m_import_group_id_str, m_import_title_id_str, m_import_title_id);
       break;
     }
     }
@@ -348,9 +343,8 @@ IPCCommandResult WFSI::IOCtl(const IOCtlRequest& request)
     SetCurrentTitleIdAndGroupId(title_id, group_id);
 
     // Change home directory
-    const std::string homedir_path =
-        StringFromFormat("/vol/%s/title/%s/%s/", m_device_name.c_str(),
-                         m_current_group_id_str.c_str(), m_current_title_id_str.c_str());
+    const std::string homedir_path = fmt::format("/vol/{}/title/{}/{}/", m_device_name,
+                                                 m_current_group_id_str, m_current_title_id_str);
     const u16 homedir_path_len = static_cast<u16>(homedir_path.size());
     INFO_LOG(IOS_WFS, "IOCTL_WFSI_CHANGE_TITLE: %s (path_len: 0x%x)", homedir_path.c_str(),
              homedir_path_len);
@@ -414,34 +408,32 @@ IPCCommandResult WFSI::IOCtl(const IOCtlRequest& request)
 
     if (m_patch_type == NOT_A_PATCH)
     {
-      std::string install_directory = StringFromFormat("/vol/%s/_install", m_device_name.c_str());
+      const std::string install_directory = fmt::format("/vol/{}/_install", m_device_name);
       if (!m_continue_install && File::IsDirectory(WFS::NativePath(install_directory)))
       {
         File::DeleteDirRecursively(WFS::NativePath(install_directory));
       }
 
-      m_base_extract_path = StringFromFormat("%s/%s/content", install_directory.c_str(),
-                                             m_import_title_id_str.c_str());
+      m_base_extract_path = fmt::format("{}/{}/content", install_directory, m_import_title_id_str);
       File::CreateFullPath(WFS::NativePath(m_base_extract_path));
       File::CreateDir(WFS::NativePath(m_base_extract_path));
 
-      for (auto dir : {"work", "meta", "save"})
+      for (const auto dir : {"work", "meta", "save"})
       {
-        std::string path = StringFromFormat("%s/%s/%s", install_directory.c_str(),
-                                            m_import_title_id_str.c_str(), dir);
+        const std::string path =
+            fmt::format("{}/{}/{}", install_directory, m_import_title_id_str, dir);
         File::CreateDir(WFS::NativePath(path));
       }
 
-      std::string group_path = StringFromFormat("/vol/%s/title/%s", m_device_name.c_str(),
-                                                m_import_group_id_str.c_str());
+      const std::string group_path =
+          fmt::format("/vol/{}/title/{}", m_device_name, m_import_group_id_str);
       File::CreateFullPath(WFS::NativePath(group_path));
       File::CreateDir(WFS::NativePath(group_path));
     }
     else
     {
-      m_base_extract_path =
-          StringFromFormat("/vol/%s/title/%s/%s/_patch/content", m_device_name.c_str(),
-                           m_current_group_id_str.c_str(), m_current_title_id_str.c_str());
+      m_base_extract_path = fmt::format("/vol/{}/title/{}/{}/_patch/content", m_device_name,
+                                        m_current_group_id_str, m_current_title_id_str);
       File::CreateFullPath(WFS::NativePath(m_base_extract_path));
       File::CreateDir(WFS::NativePath(m_base_extract_path));
     }
@@ -489,13 +481,12 @@ IPCCommandResult WFSI::IOCtl(const IOCtlRequest& request)
 
   case IOCTL_WFSI_LOAD_DOL:
   {
-    std::string path =
-        StringFromFormat("/vol/%s/title/%s/%s/content", m_device_name.c_str(),
-                         m_current_group_id_str.c_str(), m_current_title_id_str.c_str());
+    std::string path = fmt::format("/vol/{}/title/{}/{}/content", m_device_name,
+                                   m_current_group_id_str, m_current_title_id_str);
 
-    u32 dol_addr = Memory::Read_U32(request.buffer_in + 0x18);
-    u32 max_dol_size = Memory::Read_U32(request.buffer_in + 0x14);
-    u16 dol_extension_id = Memory::Read_U16(request.buffer_in + 0x1e);
+    const u32 dol_addr = Memory::Read_U32(request.buffer_in + 0x18);
+    const u32 max_dol_size = Memory::Read_U32(request.buffer_in + 0x14);
+    const u16 dol_extension_id = Memory::Read_U16(request.buffer_in + 0x1e);
 
     if (dol_extension_id == 0)
     {
@@ -503,7 +494,7 @@ IPCCommandResult WFSI::IOCtl(const IOCtlRequest& request)
     }
     else
     {
-      path += StringFromFormat("/extension%d.dol", dol_extension_id);
+      path += fmt::format("/extension{}.dol", dol_extension_id);
     }
 
     INFO_LOG(IOS_WFS, "IOCTL_WFSI_LOAD_DOL: loading %s at address %08x (size %d)", path.c_str(),
@@ -562,9 +553,8 @@ IPCCommandResult WFSI::IOCtl(const IOCtlRequest& request)
 
 u32 WFSI::GetTmd(u16 group_id, u32 title_id, u64 subtitle_id, u32 address, u32* size) const
 {
-  std::string path =
-      StringFromFormat("/vol/%s/title/%s/%s/meta/%016" PRIx64 ".tmd", m_device_name.c_str(),
-                       GroupIdStr(group_id).c_str(), TitleIdStr(title_id).c_str(), subtitle_id);
+  const std::string path = fmt::format("/vol/{}/title/{}/{}/meta/{:016x}.tmd", m_device_name,
+                                       GroupIdStr(group_id), TitleIdStr(title_id), subtitle_id);
   File::IOFile fp(WFS::NativePath(path), "rb");
   if (!fp)
   {
@@ -581,10 +571,8 @@ u32 WFSI::GetTmd(u16 group_id, u32 title_id, u64 subtitle_id, u32 address, u32*
 
 static s32 DeleteTemporaryFiles(const std::string& device_name, u64 title_id)
 {
-  File::Delete(WFS::NativePath(
-      StringFromFormat("/vol/%s/tmp/%016" PRIx64 ".ini", device_name.c_str(), title_id)));
-  File::Delete(WFS::NativePath(
-      StringFromFormat("/vol/%s/tmp/%016" PRIx64 ".ppcini", device_name.c_str(), title_id)));
+  File::Delete(WFS::NativePath(fmt::format("/vol/{}/tmp/{:016x}.ini", device_name, title_id)));
+  File::Delete(WFS::NativePath(fmt::format("/vol/{}/tmp/{:016x}.ppcini", device_name, title_id)));
   return IPC_SUCCESS;
 }
 
@@ -594,8 +582,7 @@ s32 WFSI::CancelTitleImport(bool continue_install)
 
   if (!continue_install)
   {
-    File::DeleteDirRecursively(
-        WFS::NativePath(StringFromFormat("/vol/%s/_install", m_device_name.c_str())));
+    File::DeleteDirRecursively(WFS::NativePath(fmt::format("/vol/{}/_install", m_device_name)));
   }
 
   DeleteTemporaryFiles(m_device_name, m_import_title_id);
@@ -609,16 +596,15 @@ s32 WFSI::CancelPatchImport(bool continue_install)
 
   if (!continue_install)
   {
-    File::DeleteDirRecursively(WFS::NativePath(
-        StringFromFormat("/vol/%s/title/%s/%s/_patch", m_device_name.c_str(),
-                         m_current_group_id_str.c_str(), m_current_title_id_str.c_str())));
+    File::DeleteDirRecursively(
+        WFS::NativePath(fmt::format("/vol/{}/title/{}/{}/_patch", m_device_name,
+                                    m_current_group_id_str, m_current_title_id_str)));
 
     if (m_patch_type == PatchType::PATCH_TYPE_2)
     {
       // Move back _default.dol to default.dol.
-      const std::string content_dir =
-          StringFromFormat("/vol/%s/title/%s/%s/content", m_device_name.c_str(),
-                           m_current_group_id_str.c_str(), m_current_title_id_str.c_str());
+      const std::string content_dir = fmt::format("/vol/{}/title/{}/{}/content", m_device_name,
+                                                  m_current_group_id_str, m_current_title_id_str);
       File::Rename(WFS::NativePath(content_dir + "/_default.dol"),
                    WFS::NativePath(content_dir + "/default.dol"));
     }
diff --git a/Source/Core/Core/WiiRoot.cpp b/Source/Core/Core/WiiRoot.cpp
index 78f73950a0..06be93900a 100644
--- a/Source/Core/Core/WiiRoot.cpp
+++ b/Source/Core/Core/WiiRoot.cpp
@@ -8,13 +8,14 @@
 #include <string>
 #include <vector>
 
+#include <fmt/format.h>
+
 #include "Common/CommonPaths.h"
 #include "Common/CommonTypes.h"
 #include "Common/File.h"
 #include "Common/FileUtil.h"
 #include "Common/Logging/Log.h"
 #include "Common/NandPaths.h"
-#include "Common/StringUtil.h"
 #include "Core/ConfigManager.h"
 #include "Core/HW/WiiSave.h"
 #include "Core/IOS/ES/ES.h"
@@ -268,7 +269,7 @@ void CleanUpWiiFileSystemContents()
     const auto user_save = WiiSave::MakeNandStorage(configured_fs.get(), title_id);
 
     const std::string backup_path =
-        File::GetUserPath(D_BACKUP_IDX) + StringFromFormat("/%016" PRIx64 ".bin", title_id);
+        fmt::format("{}/{:016x}.bin", File::GetUserPath(D_BACKUP_IDX), title_id);
     const auto backup_save = WiiSave::MakeDataBinStorage(&ios->GetIOSC(), backup_path, "w+b");
 
     // Backup the existing save just in case it's still needed.
diff --git a/Source/Core/Core/WiiUtils.cpp b/Source/Core/Core/WiiUtils.cpp
index 1f9052ac02..4c68509f8a 100644
--- a/Source/Core/Core/WiiUtils.cpp
+++ b/Source/Core/Core/WiiUtils.cpp
@@ -8,7 +8,6 @@
 #include <bitset>
 #include <cinttypes>
 #include <cstddef>
-#include <cstring>
 #include <map>
 #include <memory>
 #include <optional>
@@ -18,10 +17,10 @@
 #include <utility>
 #include <vector>
 
+#include <fmt/format.h>
 #include <pugixml.hpp>
 
 #include "Common/Assert.h"
-#include "Common/CommonPaths.h"
 #include "Common/CommonTypes.h"
 #include "Common/FileUtil.h"
 #include "Common/HttpRequest.h"
@@ -43,7 +42,6 @@
 #include "DiscIO/Filesystem.h"
 #include "DiscIO/Volume.h"
 #include "DiscIO/VolumeFileBlobReader.h"
-#include "DiscIO/VolumeWii.h"
 #include "DiscIO/WiiWad.h"
 
 namespace WiiUtils
@@ -232,7 +230,7 @@ std::string SystemUpdater::GetDeviceId()
   u32 ios_device_id;
   if (m_ios.GetES()->GetDeviceId(&ios_device_id) < 0)
     return "";
-  return StringFromFormat("%" PRIu64, (u64(1) << 32) | ios_device_id);
+  return std::to_string((u64(1) << 32) | ios_device_id);
 }
 
 class OnlineSystemUpdater final : public SystemUpdater
@@ -531,10 +529,9 @@ UpdateResult OnlineSystemUpdater::InstallTitleFromNUS(const std::string& prefix_
 std::pair<IOS::ES::TMDReader, std::vector<u8>>
 OnlineSystemUpdater::DownloadTMD(const std::string& prefix_url, const TitleInfo& title)
 {
-  const std::string url =
-      (title.version == 0) ?
-          prefix_url + StringFromFormat("/%016" PRIx64 "/tmd", title.id) :
-          prefix_url + StringFromFormat("/%016" PRIx64 "/tmd.%u", title.id, title.version);
+  const std::string url = (title.version == 0) ?
+                              fmt::format("{}/{:016x}/tmd", prefix_url, title.id) :
+                              fmt::format("{}/{:016x}/tmd.{}", prefix_url, title.id, title.version);
   const Common::HttpRequest::Response response = m_http.Get(url);
   if (!response)
     return {};
@@ -559,7 +556,7 @@ OnlineSystemUpdater::DownloadTMD(const std::string& prefix_url, const TitleInfo&
 std::pair<std::vector<u8>, std::vector<u8>>
 OnlineSystemUpdater::DownloadTicket(const std::string& prefix_url, const TitleInfo& title)
 {
-  const std::string url = prefix_url + StringFromFormat("/%016" PRIx64 "/cetk", title.id);
+  const std::string url = fmt::format("{}/{:016x}/cetk", prefix_url, title.id);
   const Common::HttpRequest::Response response = m_http.Get(url);
   if (!response)
     return {};
@@ -576,7 +573,7 @@ OnlineSystemUpdater::DownloadTicket(const std::string& prefix_url, const TitleIn
 std::optional<std::vector<u8>> OnlineSystemUpdater::DownloadContent(const std::string& prefix_url,
                                                                     const TitleInfo& title, u32 cid)
 {
-  const std::string url = prefix_url + StringFromFormat("/%016" PRIx64 "/%08x", title.id, cid);
+  const std::string url = fmt::format("{}/{:016x}/{:08x}", prefix_url, title.id, cid);
   return m_http.Get(url);
 }