diff --git a/Source/Core/Common/I2C.cpp b/Source/Core/Common/I2C.cpp
index aab3f7cb92..c8acb3511c 100644
--- a/Source/Core/Common/I2C.cpp
+++ b/Source/Core/Common/I2C.cpp
@@ -412,7 +412,7 @@ void I2CBus::DoState(PointerWrap& p)
 
 bool I2CSlaveAutoIncrementing::StartWrite(u8 slave_addr)
 {
-  if (slave_addr == m_slave_addr)
+  if (DeviceEnabled() && slave_addr == m_slave_addr)
   {
     INFO_LOG_FMT(WII_IPC, "I2C Device {:02x} write started, previously active: {}", m_slave_addr,
                  m_active);
@@ -428,7 +428,7 @@ bool I2CSlaveAutoIncrementing::StartWrite(u8 slave_addr)
 
 bool I2CSlaveAutoIncrementing::StartRead(u8 slave_addr)
 {
-  if (slave_addr == m_slave_addr)
+  if (DeviceEnabled() && slave_addr == m_slave_addr)
   {
     INFO_LOG_FMT(WII_IPC, "I2C Device {:02x} read started, previously active: {}", m_slave_addr,
                  m_active);
@@ -508,8 +508,6 @@ void I2CSlaveAutoIncrementing::DoState(PointerWrap& p)
   }
   p.Do(m_active);
   p.Do(m_device_address);
-
-  DoDeviceState(p);
 }
 
 };  // namespace Common
diff --git a/Source/Core/Common/I2C.h b/Source/Core/Common/I2C.h
index 61b3c518bd..e2bb96a06b 100644
--- a/Source/Core/Common/I2C.h
+++ b/Source/Core/Common/I2C.h
@@ -47,7 +47,7 @@ protected:
   }
 };
 
-class I2CSlaveAutoIncrementing : public I2CSlave
+class I2CSlaveAutoIncrementing : public virtual I2CSlave
 {
 public:
   I2CSlaveAutoIncrementing(u8 slave_addr) : m_slave_addr(slave_addr) {}
@@ -59,14 +59,14 @@ public:
   std::optional<u8> ReadByte() override;
   bool WriteByte(u8 value) override;
 
-  void DoState(PointerWrap& p);
+  virtual void DoState(PointerWrap& p);
 
 protected:
+  // i.e. should the device respond on the bus
+  virtual bool DeviceEnabled() { return true; }
   virtual u8 ReadByte(u8 addr) = 0;
   virtual void WriteByte(u8 addr, u8 value) = 0;
 
-  virtual void DoDeviceState(PointerWrap& p) = 0;
-
 private:
   const u8 m_slave_addr;
   bool m_active = false;
@@ -104,6 +104,16 @@ public:
   int BusRead(u8 slave_addr, u8 addr, int count, u8* data_out);
 };
 
+class I2CBusForwarding : public I2CBusSimple
+{
+public:
+  using I2CBusBase::ReadByte;
+  using I2CBusBase::StartRead;
+  using I2CBusBase::StartWrite;
+  using I2CBusBase::Stop;
+  using I2CBusBase::WriteByte;
+};
+
 // An I²C bus implementation accessed via bit-banging.
 // A few assumptions and limitations exist:
 // - All devices support both writes and reads.
diff --git a/Source/Core/Core/HW/WII_IPC.cpp b/Source/Core/Core/HW/WII_IPC.cpp
index 817261780b..5cf7ae22cb 100644
--- a/Source/Core/Core/HW/WII_IPC.cpp
+++ b/Source/Core/Core/HW/WII_IPC.cpp
@@ -176,6 +176,12 @@ public:
     ave_ever_logged = {};
   }
 
+  void DoState(PointerWrap& p) override
+  {
+    I2CSlaveAutoIncrementing::DoState(p);
+    p.Do(m_registers);
+  }
+
   AVEState m_registers{};
 
 protected:
@@ -203,7 +209,6 @@ protected:
                     value);
     }
   }
-  void DoDeviceState(PointerWrap& p) override { p.Do(m_registers); }
 
 private:
   std::bitset<sizeof(AVEState)> ave_ever_logged{};  // logging only, not saved
diff --git a/Source/Core/Core/HW/WiimoteEmu/Camera.cpp b/Source/Core/Core/HW/WiimoteEmu/Camera.cpp
index 1dcdb77952..14efaed6b8 100644
--- a/Source/Core/Core/HW/WiimoteEmu/Camera.cpp
+++ b/Source/Core/Core/HW/WiimoteEmu/Camera.cpp
@@ -24,31 +24,26 @@ void CameraLogic::Reset()
 
 void CameraLogic::DoState(PointerWrap& p)
 {
+  I2CSlaveAutoIncrementing::DoState(p);
+
   p.Do(m_reg_data);
 
   // FYI: m_is_enabled is handled elsewhere.
 }
 
-int CameraLogic::BusRead(u8 slave_addr, u8 addr, int count, u8* data_out)
+bool CameraLogic::DeviceEnabled()
 {
-  if (I2C_ADDR != slave_addr)
-    return 0;
-
-  if (!m_is_enabled)
-    return 0;
-
-  return RawRead(&m_reg_data, addr, count, data_out);
+  return m_is_enabled;
 }
 
-int CameraLogic::BusWrite(u8 slave_addr, u8 addr, int count, const u8* data_in)
+u8 CameraLogic::ReadByte(u8 addr)
 {
-  if (I2C_ADDR != slave_addr)
-    return 0;
+  return RawRead(&m_reg_data, addr);
+}
 
-  if (!m_is_enabled)
-    return 0;
-
-  return RawWrite(&m_reg_data, addr, count, data_in);
+void CameraLogic::WriteByte(u8 addr, u8 value)
+{
+  RawWrite(&m_reg_data, addr, value);
 }
 
 std::array<CameraPoint, CameraLogic::NUM_POINTS>
diff --git a/Source/Core/Core/HW/WiimoteEmu/Camera.h b/Source/Core/Core/HW/WiimoteEmu/Camera.h
index 23e21cc84e..6942cf12d2 100644
--- a/Source/Core/Core/HW/WiimoteEmu/Camera.h
+++ b/Source/Core/Core/HW/WiimoteEmu/Camera.h
@@ -5,8 +5,8 @@
 
 #include "Common/ChunkFile.h"
 #include "Common/CommonTypes.h"
+#include "Common/I2C.h"
 #include "Core/HW/WiimoteEmu/Dynamics.h"
-#include "Core/HW/WiimoteEmu/I2CBus.h"
 #include "InputCommon/ControllerEmu/ControlGroup/Cursor.h"
 
 namespace Common
@@ -101,9 +101,11 @@ struct IRFull : IRExtended
 };
 static_assert(sizeof(IRFull) == 9, "Wrong size");
 
-class CameraLogic : public I2CSlave
+class CameraLogic : public Common::I2CSlaveAutoIncrementing
 {
 public:
+  CameraLogic() : I2CSlaveAutoIncrementing(I2C_ADDR) {}
+
   // OEM sensor bar distance between LED clusters in meters.
   static constexpr float SENSOR_BAR_LED_SEPARATION = 0.2f;
 
@@ -132,7 +134,7 @@ public:
   static constexpr int MAX_POINT_SIZE = 15;
 
   void Reset();
-  void DoState(PointerWrap& p);
+  void DoState(PointerWrap& p) override;
   static std::array<CameraPoint, NUM_POINTS> GetCameraPoints(const Common::Matrix44& transform,
                                                              Common::Vec2 field_of_view);
   void Update(const std::array<CameraPoint, NUM_POINTS>& camera_points);
@@ -176,8 +178,9 @@ public:
   static const u8 REPORT_DATA_OFFSET = offsetof(Register, camera_data);
 
 private:
-  int BusRead(u8 slave_addr, u8 addr, int count, u8* data_out) override;
-  int BusWrite(u8 slave_addr, u8 addr, int count, const u8* data_in) override;
+  bool DeviceEnabled() override;
+  u8 ReadByte(u8 addr) override;
+  void WriteByte(u8 addr, u8 value) override;
 
   Register m_reg_data{};
 
diff --git a/Source/Core/Core/HW/WiimoteEmu/Extension/Extension.cpp b/Source/Core/Core/HW/WiimoteEmu/Extension/Extension.cpp
index fd2b185872..55e7ebecfa 100644
--- a/Source/Core/Core/HW/WiimoteEmu/Extension/Extension.cpp
+++ b/Source/Core/Core/HW/WiimoteEmu/Extension/Extension.cpp
@@ -71,14 +71,29 @@ void None::DoState(PointerWrap& p)
   // Nothing needed.
 }
 
-int None::BusRead(u8 slave_addr, u8 addr, int count, u8* data_out)
+bool None::StartWrite(u8 slave_addr)
 {
-  return 0;
+  return false;
 }
 
-int None::BusWrite(u8 slave_addr, u8 addr, int count, const u8* data_in)
+bool None::StartRead(u8 slave_addr)
 {
-  return 0;
+  return false;
+}
+
+void None::Stop()
+{
+  // Nothing needed.
+}
+
+std::optional<u8> None::ReadByte()
+{
+  return std::nullopt;
+}
+
+bool None::WriteByte(u8 value)
+{
+  return false;
 }
 
 bool EncryptedExtension::ReadDeviceDetectPin() const
@@ -86,11 +101,8 @@ bool EncryptedExtension::ReadDeviceDetectPin() const
   return true;
 }
 
-int EncryptedExtension::BusRead(u8 slave_addr, u8 addr, int count, u8* data_out)
+u8 EncryptedExtension::ReadByte(u8 addr)
 {
-  if (I2C_ADDR != slave_addr)
-    return 0;
-
   if (0x00 == addr)
   {
     // This is where real hardware would update controller data
@@ -98,7 +110,7 @@ int EncryptedExtension::BusRead(u8 slave_addr, u8 addr, int count, u8* data_out)
     // TAS code fails to sync data reads and such..
   }
 
-  auto const result = RawRead(&m_reg, addr, count, data_out);
+  u8 result = RawRead(&m_reg, addr);
 
   // Encrypt data read from extension register.
   if (ENCRYPTION_ENABLED == m_reg.encryption)
@@ -109,30 +121,25 @@ int EncryptedExtension::BusRead(u8 slave_addr, u8 addr, int count, u8* data_out)
       m_is_key_dirty = false;
     }
 
-    ext_key.Encrypt(data_out, addr, count);
+    ext_key.Encrypt(&result, addr, 1);
   }
 
   return result;
 }
 
-int EncryptedExtension::BusWrite(u8 slave_addr, u8 addr, int count, const u8* data_in)
+void EncryptedExtension::WriteByte(u8 addr, u8 value)
 {
-  if (I2C_ADDR != slave_addr)
-    return 0;
-
-  auto const result = RawWrite(&m_reg, addr, count, data_in);
+  RawWrite(&m_reg, addr, value);
 
   constexpr u8 ENCRYPTION_KEY_DATA_BEGIN = offsetof(Register, encryption_key_data);
   constexpr u8 ENCRYPTION_KEY_DATA_END = ENCRYPTION_KEY_DATA_BEGIN + 0x10;
 
-  if (addr + count > ENCRYPTION_KEY_DATA_BEGIN && addr < ENCRYPTION_KEY_DATA_END)
+  if (addr >= ENCRYPTION_KEY_DATA_BEGIN && addr < ENCRYPTION_KEY_DATA_END)
   {
     // FYI: Real extensions seem to require the key data written in specifically sized chunks.
     // We just run the key generation on all writes to the key area.
     m_is_key_dirty = true;
   }
-
-  return result;
 }
 
 void EncryptedExtension::Reset()
@@ -147,6 +154,8 @@ void EncryptedExtension::Reset()
 
 void EncryptedExtension::DoState(PointerWrap& p)
 {
+  I2CSlaveAutoIncrementing::DoState(p);
+
   p.Do(m_reg);
 
   if (p.IsReadMode())
diff --git a/Source/Core/Core/HW/WiimoteEmu/Extension/Extension.h b/Source/Core/Core/HW/WiimoteEmu/Extension/Extension.h
index 4a055c597d..bafab30a06 100644
--- a/Source/Core/Core/HW/WiimoteEmu/Extension/Extension.h
+++ b/Source/Core/Core/HW/WiimoteEmu/Extension/Extension.h
@@ -10,15 +10,19 @@
 
 #include "Common/ChunkFile.h"
 #include "Common/CommonTypes.h"
+#include "Common/I2C.h"
 #include "Core/HW/WiimoteEmu/Encryption.h"
-#include "Core/HW/WiimoteEmu/I2CBus.h"
 #include "InputCommon/ControllerEmu/ControllerEmu.h"
 
+#ifdef _MSC_VER
+#pragma warning(disable : 4250)  // C4250 inherits via dominance - intended behavior here
+#endif
+
 namespace WiimoteEmu
 {
 struct DesiredExtensionState;
 
-class Extension : public ControllerEmu::EmulatedController, public I2CSlave
+class Extension : public ControllerEmu::EmulatedController, public virtual Common::I2CSlave
 {
 public:
   explicit Extension(const char* name);
@@ -56,23 +60,39 @@ private:
   void Reset() override;
   void DoState(PointerWrap& p) override;
 
-  int BusRead(u8 slave_addr, u8 addr, int count, u8* data_out) override;
-  int BusWrite(u8 slave_addr, u8 addr, int count, const u8* data_in) override;
+  bool StartWrite(u8 slave_addr) override;
+  bool StartRead(u8 slave_addr) override;
+  void Stop() override;
+  std::optional<u8> ReadByte() override;
+  bool WriteByte(u8 value) override;
 };
 
 // This class provides the encryption and initialization behavior of most extensions.
-class EncryptedExtension : public Extension
+class EncryptedExtension : public Extension, public Common::I2CSlaveAutoIncrementing
 {
 public:
   static constexpr u8 I2C_ADDR = 0x52;
   static constexpr int CONTROLLER_DATA_BYTES = 21;
 
-  using Extension::Extension;
+  explicit EncryptedExtension(const char* name)
+      : Extension(name), I2CSlaveAutoIncrementing(I2C_ADDR)
+  {
+  }
+  EncryptedExtension(const char* config_name, const char* display_name)
+      : Extension(config_name, display_name), I2CSlaveAutoIncrementing(I2C_ADDR)
+  {
+  }
 
   // TODO: This is public for TAS reasons.
   // TODO: TAS handles encryption poorly.
   EncryptionKey ext_key;
 
+  using I2CSlaveAutoIncrementing::ReadByte;
+  using I2CSlaveAutoIncrementing::StartRead;
+  using I2CSlaveAutoIncrementing::StartWrite;
+  using I2CSlaveAutoIncrementing::Stop;
+  using I2CSlaveAutoIncrementing::WriteByte;
+
   static constexpr int CALIBRATION_CHECKSUM_BYTES = 2;
 
 #pragma pack(push, 1)
@@ -117,8 +137,8 @@ private:
 
   bool ReadDeviceDetectPin() const override;
 
-  int BusRead(u8 slave_addr, u8 addr, int count, u8* data_out) override;
-  int BusWrite(u8 slave_addr, u8 addr, int count, const u8* data_in) override;
+  u8 ReadByte(u8 addr) override;
+  void WriteByte(u8 addr, u8 value) override;
 };
 
 class Extension1stParty : public EncryptedExtension
diff --git a/Source/Core/Core/HW/WiimoteEmu/ExtensionPort.cpp b/Source/Core/Core/HW/WiimoteEmu/ExtensionPort.cpp
index 97e73ea4bc..2b152686b8 100644
--- a/Source/Core/Core/HW/WiimoteEmu/ExtensionPort.cpp
+++ b/Source/Core/Core/HW/WiimoteEmu/ExtensionPort.cpp
@@ -7,7 +7,7 @@
 
 namespace WiimoteEmu
 {
-ExtensionPort::ExtensionPort(I2CBus* i2c_bus) : m_i2c_bus(*i2c_bus)
+ExtensionPort::ExtensionPort(Common::I2CBusBase* i2c_bus) : m_i2c_bus(*i2c_bus)
 {
 }
 
diff --git a/Source/Core/Core/HW/WiimoteEmu/ExtensionPort.h b/Source/Core/Core/HW/WiimoteEmu/ExtensionPort.h
index 86b1fd31f9..bb2f0ec012 100644
--- a/Source/Core/Core/HW/WiimoteEmu/ExtensionPort.h
+++ b/Source/Core/Core/HW/WiimoteEmu/ExtensionPort.h
@@ -4,8 +4,8 @@
 #pragma once
 
 #include "Common/ChunkFile.h"
+#include "Common/I2C.h"
 #include "Core/HW/WiimoteEmu/Extension/Extension.h"
-#include "Core/HW/WiimoteEmu/I2CBus.h"
 
 namespace WiimoteEmu
 {
@@ -35,14 +35,14 @@ public:
   static constexpr u8 REPORT_I2C_SLAVE = 0x52;
   static constexpr u8 REPORT_I2C_ADDR = 0x00;
 
-  explicit ExtensionPort(I2CBus* i2c_bus);
+  explicit ExtensionPort(Common::I2CBusBase* i2c_bus);
 
   bool IsDeviceConnected() const;
   void AttachExtension(Extension* dev);
 
 private:
   Extension* m_extension = nullptr;
-  I2CBus& m_i2c_bus;
+  Common::I2CBusBase& m_i2c_bus;
 };
 
 }  // namespace WiimoteEmu
diff --git a/Source/Core/Core/HW/WiimoteEmu/I2CBus.cpp b/Source/Core/Core/HW/WiimoteEmu/I2CBus.cpp
index 19202350fd..e69de29bb2 100644
--- a/Source/Core/Core/HW/WiimoteEmu/I2CBus.cpp
+++ b/Source/Core/Core/HW/WiimoteEmu/I2CBus.cpp
@@ -1,53 +0,0 @@
-// Copyright 2019 Dolphin Emulator Project
-// SPDX-License-Identifier: GPL-2.0-or-later
-
-#include "Core/HW/WiimoteEmu/I2CBus.h"
-
-#include <algorithm>
-
-namespace WiimoteEmu
-{
-void I2CBus::AddSlave(I2CSlave* slave)
-{
-  m_slaves.emplace_back(slave);
-}
-
-void I2CBus::RemoveSlave(I2CSlave* slave)
-{
-  m_slaves.erase(std::remove(m_slaves.begin(), m_slaves.end(), slave), m_slaves.end());
-}
-
-void I2CBus::Reset()
-{
-  m_slaves.clear();
-}
-
-int I2CBus::BusRead(u8 slave_addr, u8 addr, int count, u8* data_out)
-{
-  for (auto& slave : m_slaves)
-  {
-    auto const bytes_read = slave->BusRead(slave_addr, addr, count, data_out);
-
-    // A slave responded, we are done.
-    if (bytes_read)
-      return bytes_read;
-  }
-
-  return 0;
-}
-
-int I2CBus::BusWrite(u8 slave_addr, u8 addr, int count, const u8* data_in)
-{
-  for (auto& slave : m_slaves)
-  {
-    auto const bytes_written = slave->BusWrite(slave_addr, addr, count, data_in);
-
-    // A slave responded, we are done.
-    if (bytes_written)
-      return bytes_written;
-  }
-
-  return 0;
-}
-
-}  // namespace WiimoteEmu
diff --git a/Source/Core/Core/HW/WiimoteEmu/I2CBus.h b/Source/Core/Core/HW/WiimoteEmu/I2CBus.h
index 3a1e0a67d3..e69de29bb2 100644
--- a/Source/Core/Core/HW/WiimoteEmu/I2CBus.h
+++ b/Source/Core/Core/HW/WiimoteEmu/I2CBus.h
@@ -1,75 +0,0 @@
-// Copyright 2019 Dolphin Emulator Project
-// SPDX-License-Identifier: GPL-2.0-or-later
-
-#pragma once
-
-#include <algorithm>
-#include <vector>
-
-#include "Common/CommonTypes.h"
-
-namespace WiimoteEmu
-{
-class I2CBus;
-
-class I2CSlave
-{
-  friend I2CBus;
-
-protected:
-  virtual ~I2CSlave() = default;
-
-  virtual int BusRead(u8 slave_addr, u8 addr, int count, u8* data_out) = 0;
-  virtual int BusWrite(u8 slave_addr, u8 addr, int count, const u8* data_in) = 0;
-
-  template <typename T>
-  static int RawRead(T* reg_data, u8 addr, int count, u8* data_out)
-  {
-    static_assert(std::is_standard_layout_v<T> && std::is_trivially_copyable_v<T>);
-    static_assert(0x100 == sizeof(T));
-
-    // TODO: addr wraps around after 0xff
-
-    u8* src = reinterpret_cast<u8*>(reg_data) + addr;
-    count = std::min(count, int(reinterpret_cast<u8*>(reg_data + 1) - src));
-
-    std::copy_n(src, count, data_out);
-
-    return count;
-  }
-
-  template <typename T>
-  static int RawWrite(T* reg_data, u8 addr, int count, const u8* data_in)
-  {
-    static_assert(std::is_standard_layout_v<T> && std::is_trivially_copyable_v<T>);
-    static_assert(0x100 == sizeof(T));
-
-    // TODO: addr wraps around after 0xff
-
-    u8* dst = reinterpret_cast<u8*>(reg_data) + addr;
-    count = std::min(count, int(reinterpret_cast<u8*>(reg_data + 1) - dst));
-
-    std::copy_n(data_in, count, dst);
-
-    return count;
-  }
-};
-
-class I2CBus
-{
-public:
-  void AddSlave(I2CSlave* slave);
-  void RemoveSlave(I2CSlave* slave);
-
-  void Reset();
-
-  // TODO: change int to u16 or something
-  int BusRead(u8 slave_addr, u8 addr, int count, u8* data_out);
-  int BusWrite(u8 slave_addr, u8 addr, int count, const u8* data_in);
-
-private:
-  // Pointers are unowned:
-  std::vector<I2CSlave*> m_slaves;
-};
-
-}  // namespace WiimoteEmu
diff --git a/Source/Core/Core/HW/WiimoteEmu/MotionPlus.cpp b/Source/Core/Core/HW/WiimoteEmu/MotionPlus.cpp
index 9dc3b2ad1c..f7c5ab50a0 100644
--- a/Source/Core/Core/HW/WiimoteEmu/MotionPlus.cpp
+++ b/Source/Core/Core/HW/WiimoteEmu/MotionPlus.cpp
@@ -189,135 +189,187 @@ ExtensionPort& MotionPlus::GetExtPort()
   return m_extension_port;
 }
 
-int MotionPlus::BusRead(u8 slave_addr, u8 addr, int count, u8* data_out)
+bool MotionPlus::StartWrite(u8 slave_addr)
 {
   switch (GetActivationStatus())
   {
   case ActivationStatus::Inactive:
-    if (INACTIVE_DEVICE_ADDR != slave_addr)
-    {
-      // Passthrough to the connected extension. (if any)
-      return m_i2c_bus.BusRead(slave_addr, addr, count, data_out);
-    }
-
-    // Perform a normal read of the M+ register.
-    return RawRead(&m_reg_data, addr, count, data_out);
+    // m_inactive_wrapper is connected to the bus, so it will respond to 0x53 when inactive.
+    return m_i2c_bus.StartWrite(slave_addr);
 
   case ActivationStatus::Active:
     // FYI: Motion plus does not respond to 0x53 when activated.
-    if (ACTIVE_DEVICE_ADDR != slave_addr)
-    {
-      // No i2c passthrough when activated.
-      return 0;
-    }
-
-    // Perform a normal read of the M+ register.
-    return RawRead(&m_reg_data, addr, count, data_out);
+    // No i2c passthrough when activated, so *only* target 0x52.
+    return m_active_wrapper.StartWrite(slave_addr);
 
   default:
   case ActivationStatus::Activating:
   case ActivationStatus::Deactivating:
     // The extension port is completely unresponsive here.
-    return 0;
+    return false;
   }
 }
 
-int MotionPlus::BusWrite(u8 slave_addr, u8 addr, int count, const u8* data_in)
+bool MotionPlus::StartRead(u8 slave_addr)
 {
   switch (GetActivationStatus())
   {
   case ActivationStatus::Inactive:
-  {
-    if (INACTIVE_DEVICE_ADDR != slave_addr)
-    {
-      // Passthrough to the connected extension. (if any)
-      return m_i2c_bus.BusWrite(slave_addr, addr, count, data_in);
-    }
-
-    DEBUG_LOG_FMT(WIIMOTE, "Inactive M+ write {:#x} : {}", addr, ArrayToString(data_in, count));
-
-    auto const result = RawWrite(&m_reg_data, addr, count, data_in);
-
-    if (PASSTHROUGH_MODE_OFFSET == addr)
-    {
-      OnPassthroughModeWrite();
-    }
-
-    return result;
-  }
+    // m_inactive_wrapper is connected to the bus, so it will respond to 0x53 when inactive.
+    return m_i2c_bus.StartRead(slave_addr);
 
   case ActivationStatus::Active:
-  {
     // FYI: Motion plus does not respond to 0x53 when activated.
-    if (ACTIVE_DEVICE_ADDR != slave_addr)
-    {
-      // No i2c passthrough when activated.
-      return 0;
-    }
-
-    DEBUG_LOG_FMT(WIIMOTE, "Active M+ write {:#x} : {}", addr, ArrayToString(data_in, count));
-
-    auto const result = RawWrite(&m_reg_data, addr, count, data_in);
-
-    switch (addr)
-    {
-    case offsetof(Register, init_trigger):
-      // It seems a write of any value here triggers deactivation on a real M+.
-      Deactivate();
-
-      // Passthrough the write to the attached extension.
-      // The M+ deactivation signal is cleverly the same as EXT initialization.
-      m_i2c_bus.BusWrite(slave_addr, addr, count, data_in);
-      break;
-
-    case offsetof(Register, challenge_type):
-      if (ChallengeState::ParameterXReady == m_reg_data.challenge_state)
-      {
-        DEBUG_LOG_FMT(WIIMOTE, "M+ challenge: {:#x}", m_reg_data.challenge_type);
-
-        // After games read parameter x they write here to request y0 or y1.
-        if (0 == m_reg_data.challenge_type)
-        {
-          // Preparing y0 on the real M+ is almost instant (30ms maybe).
-          constexpr int PREPARE_Y0_MS = 30;
-          m_progress_timer = ::Wiimote::UPDATE_FREQ * PREPARE_Y0_MS / 1000;
-        }
-        else
-        {
-          // A real M+ takes about 1200ms to prepare y1.
-          // Games seem to not care that we don't take that long.
-          constexpr int PREPARE_Y1_MS = 500;
-          m_progress_timer = ::Wiimote::UPDATE_FREQ * PREPARE_Y1_MS / 1000;
-        }
-
-        // Games give the M+ a bit of time to compute the value.
-        // y0 gets about half a second.
-        // y1 gets at about 9.5 seconds.
-        // After this the M+ will fail the "challenge".
-
-        m_reg_data.challenge_state = ChallengeState::PreparingY;
-      }
-      break;
-
-    case offsetof(Register, calibration_trigger):
-      // Games seem to invoke this to start and stop calibration. Exact consequences unknown.
-      DEBUG_LOG_FMT(WIIMOTE, "M+ calibration trigger: {:#x}", m_reg_data.calibration_trigger);
-      break;
-
-    case PASSTHROUGH_MODE_OFFSET:
-      // Games sometimes (not often) write zero here to deactivate the M+.
-      OnPassthroughModeWrite();
-      break;
-    }
-
-    return result;
-  }
+    // No i2c passthrough when activated, so *only* target 0x52.
+    return m_active_wrapper.StartRead(slave_addr);
 
   default:
   case ActivationStatus::Activating:
   case ActivationStatus::Deactivating:
     // The extension port is completely unresponsive here.
-    return 0;
+    return false;
+  }
+}
+
+void MotionPlus::Stop()
+{
+  switch (GetActivationStatus())
+  {
+  case ActivationStatus::Inactive:
+    // m_inactive_wrapper is connected to the bus, so it will respond to 0x53 when inactive.
+    m_i2c_bus.Stop();
+    break;
+
+  case ActivationStatus::Active:
+    // FYI: Motion plus does not respond to 0x53 when activated.
+    // No i2c passthrough when activated, so *only* target 0x52.
+    m_active_wrapper.Stop();
+    break;
+
+  default:
+  case ActivationStatus::Activating:
+  case ActivationStatus::Deactivating:
+    // The extension port is completely unresponsive here.
+    break;
+  }
+}
+
+std::optional<u8> MotionPlus::ReadByte()
+{
+  switch (GetActivationStatus())
+  {
+  case ActivationStatus::Inactive:
+    // m_inactive_wrapper is connected to the bus, so it will respond to 0x53 when inactive.
+    return m_i2c_bus.ReadByte();
+
+  case ActivationStatus::Active:
+    // FYI: Motion plus does not respond to 0x53 when activated.
+    // No i2c passthrough when activated, so *only* target 0x52.
+    return m_active_wrapper.ReadByte();
+
+  default:
+  case ActivationStatus::Activating:
+  case ActivationStatus::Deactivating:
+    // The extension port is completely unresponsive here.
+    return std::nullopt;
+  }
+}
+
+bool MotionPlus::WriteByte(u8 value)
+{
+  switch (GetActivationStatus())
+  {
+  case ActivationStatus::Inactive:
+    // m_inactive_wrapper is connected to the bus, so it will respond to 0x53 when inactive.
+    return m_i2c_bus.WriteByte(value);
+
+  case ActivationStatus::Active:
+    // FYI: Motion plus does not respond to 0x53 when activated.
+    // No i2c passthrough when activated, so *only* target 0x52.
+    return m_active_wrapper.WriteByte(value);
+
+  default:
+  case ActivationStatus::Activating:
+  case ActivationStatus::Deactivating:
+    // The extension port is completely unresponsive here.
+    return false;
+  }
+}
+
+u8 MotionPlus::RegisterWrapper::ReadByte(u8 addr)
+{
+  return RawRead(&m_owner->m_reg_data, addr);
+}
+
+void MotionPlus::InactiveRegisterWrapper::WriteByte(u8 addr, u8 value)
+{
+  DEBUG_LOG_FMT(WIIMOTE, "Inactive M+ write {:02x} = {:02x}", addr, value);
+
+  RawWrite(&m_owner->m_reg_data, addr, value);
+
+  if (PASSTHROUGH_MODE_OFFSET == addr)
+  {
+    m_owner->OnPassthroughModeWrite();
+  }
+}
+
+void MotionPlus::ActiveRegisterWrapper::WriteByte(u8 addr, u8 value)
+{
+  DEBUG_LOG_FMT(WIIMOTE, "Inactive M+ write {:02x} = {:02x}", addr, value);
+
+  RawWrite(&m_owner->m_reg_data, addr, value);
+
+  switch (addr)
+  {
+  case offsetof(Register, init_trigger):
+    // It seems a write of any value here triggers deactivation on a real M+.
+    m_owner->Deactivate();
+
+    // Passthrough the write to the attached extension.
+    // The M+ deactivation signal is cleverly the same as EXT initialization.
+    // TODO
+    // m_i2c_bus.BusWrite(slave_addr, addr, count, data_in);
+    break;
+
+  case offsetof(Register, challenge_type):
+    if (ChallengeState::ParameterXReady == m_owner->m_reg_data.challenge_state)
+    {
+      DEBUG_LOG_FMT(WIIMOTE, "M+ challenge: {:#x}", m_owner->m_reg_data.challenge_type);
+
+      // After games read parameter x they write here to request y0 or y1.
+      if (0 == m_owner->m_reg_data.challenge_type)
+      {
+        // Preparing y0 on the real M+ is almost instant (30ms maybe).
+        constexpr int PREPARE_Y0_MS = 30;
+        m_owner->m_progress_timer = ::Wiimote::UPDATE_FREQ * PREPARE_Y0_MS / 1000;
+      }
+      else
+      {
+        // A real M+ takes about 1200ms to prepare y1.
+        // Games seem to not care that we don't take that long.
+        constexpr int PREPARE_Y1_MS = 500;
+        m_owner->m_progress_timer = ::Wiimote::UPDATE_FREQ * PREPARE_Y1_MS / 1000;
+      }
+
+      // Games give the M+ a bit of time to compute the value.
+      // y0 gets about half a second.
+      // y1 gets at about 9.5 seconds.
+      // After this the M+ will fail the "challenge".
+
+      m_owner->m_reg_data.challenge_state = ChallengeState::PreparingY;
+    }
+    break;
+
+  case offsetof(Register, calibration_trigger):
+    // Games seem to invoke this to start and stop calibration. Exact consequences unknown.
+    DEBUG_LOG_FMT(WIIMOTE, "M+ calibration trigger: {:#x}",
+                  m_owner->m_reg_data.calibration_trigger);
+    break;
+
+  case PASSTHROUGH_MODE_OFFSET:
+    // Games sometimes (not often) write zero here to deactivate the M+.
+    m_owner->OnPassthroughModeWrite();
+    break;
   }
 }
 
diff --git a/Source/Core/Core/HW/WiimoteEmu/MotionPlus.h b/Source/Core/Core/HW/WiimoteEmu/MotionPlus.h
index 02ddfb7ec2..db6bcb089b 100644
--- a/Source/Core/Core/HW/WiimoteEmu/MotionPlus.h
+++ b/Source/Core/Core/HW/WiimoteEmu/MotionPlus.h
@@ -6,15 +6,15 @@
 #include <array>
 
 #include "Common/CommonTypes.h"
+#include "Common/I2C.h"
 #include "Common/MathUtil.h"
 #include "Common/Swap.h"
 #include "Core/HW/WiimoteEmu/Dynamics.h"
 #include "Core/HW/WiimoteEmu/ExtensionPort.h"
-#include "Core/HW/WiimoteEmu/I2CBus.h"
 
 namespace WiimoteEmu
 {
-struct MotionPlus : public Extension
+class MotionPlus : public Extension
 {
 public:
   enum class PassthroughMode : u8
@@ -241,6 +241,43 @@ private:
 #pragma pack(pop)
   static_assert(0x100 == sizeof(Register), "Wrong size");
 
+  class RegisterWrapper : public Common::I2CSlaveAutoIncrementing
+  {
+  protected:
+    RegisterWrapper(MotionPlus* owner, u8 slave_addr)
+        : I2CSlaveAutoIncrementing(slave_addr), m_owner(owner)
+    {
+    }
+
+    u8 ReadByte(u8 addr) override;
+
+    MotionPlus* const m_owner;
+  };
+
+  class InactiveRegisterWrapper : public RegisterWrapper
+  {
+  public:
+    InactiveRegisterWrapper(MotionPlus* owner) : RegisterWrapper(owner, INACTIVE_DEVICE_ADDR) {}
+
+    using Common::I2CSlaveAutoIncrementing::ReadByte;
+    using Common::I2CSlaveAutoIncrementing::WriteByte;
+
+  protected:
+    void WriteByte(u8 addr, u8 value) override;
+  };
+
+  class ActiveRegisterWrapper : public RegisterWrapper
+  {
+  public:
+    ActiveRegisterWrapper(MotionPlus* owner) : RegisterWrapper(owner, ACTIVE_DEVICE_ADDR) {}
+
+    using Common::I2CSlaveAutoIncrementing::ReadByte;
+    using Common::I2CSlaveAutoIncrementing::WriteByte;
+
+  protected:
+    void WriteByte(u8 addr, u8 value) override;
+  };
+
   void Activate();
   void Deactivate();
   void OnPassthroughModeWrite();
@@ -248,8 +285,11 @@ private:
   ActivationStatus GetActivationStatus() const;
   PassthroughMode GetPassthroughMode() const;
 
-  int BusRead(u8 slave_addr, u8 addr, int count, u8* data_out) override;
-  int BusWrite(u8 slave_addr, u8 addr, int count, const u8* data_in) override;
+  bool StartWrite(u8 slave_addr) override;
+  bool StartRead(u8 slave_addr) override;
+  void Stop() override;
+  std::optional<u8> ReadByte() override;
+  bool WriteByte(u8 value) override;
 
   bool ReadDeviceDetectPin() const override;
 
@@ -259,7 +299,10 @@ private:
   u8 m_progress_timer = {};
 
   // The port on the end of the motion plus:
-  I2CBus m_i2c_bus;
+  Common::I2CBusForwarding m_i2c_bus;
   ExtensionPort m_extension_port{&m_i2c_bus};
+
+  InactiveRegisterWrapper m_inactive_wrapper{this};  // connected to m_i2c_bus
+  ActiveRegisterWrapper m_active_wrapper{this};      // *not* connected to m_i2c_bus
 };
 }  // namespace WiimoteEmu
diff --git a/Source/Core/Core/HW/WiimoteEmu/Speaker.cpp b/Source/Core/Core/HW/WiimoteEmu/Speaker.cpp
index 23cba6bfd7..6fe6cfb0e7 100644
--- a/Source/Core/Core/HW/WiimoteEmu/Speaker.cpp
+++ b/Source/Core/Core/HW/WiimoteEmu/Speaker.cpp
@@ -146,6 +146,8 @@ void SpeakerLogic::DoState(PointerWrap& p)
 {
   p.Do(adpcm_state);
   p.Do(reg_data);
+  p.Do(m_i2c_active);
+  p.Do(m_device_address);
 }
 
 void SpeakerLogic::SetSpeakerEnabled(bool enabled)
@@ -153,29 +155,104 @@ void SpeakerLogic::SetSpeakerEnabled(bool enabled)
   m_speaker_enabled = enabled;
 }
 
-int SpeakerLogic::BusRead(u8 slave_addr, u8 addr, int count, u8* data_out)
+bool SpeakerLogic::StartWrite(u8 slave_addr)
 {
-  if (I2C_ADDR != slave_addr)
-    return 0;
-
-  return RawRead(&reg_data, addr, count, data_out);
-}
-
-int SpeakerLogic::BusWrite(u8 slave_addr, u8 addr, int count, const u8* data_in)
-{
-  if (I2C_ADDR != slave_addr)
-    return 0;
-
-  if (0x00 == addr)
+  if (slave_addr == I2C_ADDR)
   {
-    SpeakerData(data_in, count, m_speaker_pan_setting.GetValue() / 100);
-    return count;
+    INFO_LOG_FMT(WII_IPC, "I2C Device {:02x} write started, previously active: {}", I2C_ADDR,
+                 m_i2c_active);
+    m_i2c_active = true;
+    m_device_address.reset();
+    return true;
   }
   else
   {
-    // TODO: Does writing immediately change the decoder config even when active
-    // or does a write to 0x08 activate the new configuration or something?
-    return RawWrite(&reg_data, addr, count, data_in);
+    return false;
+  }
+}
+
+bool SpeakerLogic::StartRead(u8 slave_addr)
+{
+  if (slave_addr == I2C_ADDR)
+  {
+    INFO_LOG_FMT(WII_IPC, "I2C Device {:02x} read started, previously active: {}", I2C_ADDR,
+                 m_i2c_active);
+    if (m_device_address.has_value())
+    {
+      m_i2c_active = true;
+      return true;
+    }
+    else
+    {
+      WARN_LOG_FMT(WII_IPC,
+                   "I2C Device {:02x}: read attempted without having written device address",
+                   I2C_ADDR);
+      m_i2c_active = false;
+      return false;
+    }
+  }
+  else
+  {
+    return false;
+  }
+}
+
+void SpeakerLogic::Stop()
+{
+  m_i2c_active = false;
+  m_device_address.reset();
+}
+
+std::optional<u8> SpeakerLogic::ReadByte()
+{
+  if (m_i2c_active)
+  {
+    // TODO: It seems reading address 0x00 should always return 0xff.
+
+    ASSERT(m_device_address.has_value());  // enforced by StartRead
+    const u8 cur_addr = m_device_address.value();
+    // Wrapping from 255 to 0 is the assumed behavior; this may not make sense here
+    m_device_address = cur_addr + 1;
+    return RawRead(&reg_data, cur_addr);
+  }
+  else
+  {
+    return std::nullopt;
+  }
+}
+
+bool SpeakerLogic::WriteByte(u8 value)
+{
+  if (m_i2c_active)
+  {
+    if (m_device_address.has_value())
+    {
+      const u8 cur_addr = m_device_address.value();
+
+      if (cur_addr == SPEAKER_DATA_OFFSET)  // == 0
+      {
+        // Note: No auto-incrementation in this case
+        SpeakerData(&value, 1, m_speaker_pan_setting.GetValue() / 100);
+      }
+      else
+      {
+        // Wrapping from 255 to 0 is the assumed behavior; this may not make sense here
+        m_device_address = cur_addr + 1;
+
+        // TODO: Does writing immediately change the decoder config even when active
+        // or does a write to 0x08 activate the new configuration or something?
+        RawWrite(&reg_data, cur_addr, value);
+      }
+    }
+    else
+    {
+      m_device_address = value;
+    }
+    return true;
+  }
+  else
+  {
+    return false;
   }
 }
 
diff --git a/Source/Core/Core/HW/WiimoteEmu/Speaker.h b/Source/Core/Core/HW/WiimoteEmu/Speaker.h
index 9a6a652bb1..dcb93bca49 100644
--- a/Source/Core/Core/HW/WiimoteEmu/Speaker.h
+++ b/Source/Core/Core/HW/WiimoteEmu/Speaker.h
@@ -5,7 +5,7 @@
 
 #include "Common/ChunkFile.h"
 #include "Common/CommonTypes.h"
-#include "Core/HW/WiimoteEmu/I2CBus.h"
+#include "Common/I2C.h"
 #include "InputCommon/ControllerEmu/Setting/NumericSetting.h"
 
 namespace WiimoteEmu
@@ -17,7 +17,7 @@ struct ADPCMState
 
 class Wiimote;
 
-class SpeakerLogic : public I2CSlave
+class SpeakerLogic : public Common::I2CSlave
 {
   friend class Wiimote;
 
@@ -63,8 +63,11 @@ private:
 
   static_assert(0x100 == sizeof(Register));
 
-  int BusRead(u8 slave_addr, u8 addr, int count, u8* data_out) override;
-  int BusWrite(u8 slave_addr, u8 addr, int count, const u8* data_in) override;
+  bool StartWrite(u8 slave_addr) override;
+  bool StartRead(u8 slave_addr) override;
+  void Stop() override;
+  std::optional<u8> ReadByte() override;
+  bool WriteByte(u8 value) override;
 
   Register reg_data{};
 
@@ -75,6 +78,9 @@ private:
   ControllerEmu::SettingValue<double> m_speaker_pan_setting;
 
   bool m_speaker_enabled = false;
+
+  bool m_i2c_active = false;
+  std::optional<u8> m_device_address = std::nullopt;
 };
 
 }  // namespace WiimoteEmu
diff --git a/Source/Core/Core/HW/WiimoteEmu/WiimoteEmu.h b/Source/Core/Core/HW/WiimoteEmu/WiimoteEmu.h
index e364ccdb6c..8468e4dc60 100644
--- a/Source/Core/Core/HW/WiimoteEmu/WiimoteEmu.h
+++ b/Source/Core/Core/HW/WiimoteEmu/WiimoteEmu.h
@@ -10,6 +10,7 @@
 
 #include "Common/Common.h"
 #include "Common/Config/Config.h"
+#include "Common/I2C.h"
 
 #include "Core/HW/WiimoteCommon/WiimoteReport.h"
 
@@ -17,7 +18,6 @@
 #include "Core/HW/WiimoteEmu/Dynamics.h"
 #include "Core/HW/WiimoteEmu/Encryption.h"
 #include "Core/HW/WiimoteEmu/ExtensionPort.h"
-#include "Core/HW/WiimoteEmu/I2CBus.h"
 #include "Core/HW/WiimoteEmu/MotionPlus.h"
 #include "Core/HW/WiimoteEmu/Speaker.h"
 
@@ -316,7 +316,7 @@ private:
   MotionPlus m_motion_plus;
   CameraLogic m_camera_logic;
 
-  I2CBus m_i2c_bus;
+  Common::I2CBusSimple m_i2c_bus;
 
   ExtensionPort m_extension_port{&m_i2c_bus};