diff --git a/mu3hook/config.c b/mu3hook/config.c
index c611131..24086d8 100644
--- a/mu3hook/config.c
+++ b/mu3hook/config.c
@@ -10,6 +10,22 @@
 
 #include "platform/config.h"
 
+void mu3_dll_config_load(
+        struct mu3_dll_config *cfg,
+        const wchar_t *filename)
+{
+    assert(cfg != NULL);
+    assert(filename != NULL);
+
+    GetPrivateProfileStringW(
+            L"mu3io",
+            L"path",
+            L"",
+            cfg->path,
+            _countof(cfg->path),
+            filename);
+}
+
 void mu3_hook_config_load(
         struct mu3_hook_config *cfg,
         const wchar_t *filename)
@@ -20,4 +36,5 @@ void mu3_hook_config_load(
     platform_config_load(&cfg->platform, filename);
     aime_config_load(&cfg->aime, filename);
     gfx_config_load(&cfg->gfx, filename);
+    mu3_dll_config_load(&cfg->dll, filename);
 }
diff --git a/mu3hook/config.h b/mu3hook/config.h
index e6ef4df..6b2afaa 100644
--- a/mu3hook/config.h
+++ b/mu3hook/config.h
@@ -6,14 +6,21 @@
 
 #include "hooklib/gfx.h"
 
+#include "mu3hook/mu3-dll.h"
+
 #include "platform/config.h"
 
 struct mu3_hook_config {
     struct platform_config platform;
     struct aime_config aime;
     struct gfx_config gfx;
+    struct mu3_dll_config dll;
 };
 
+void mu3_dll_config_load(
+        struct mu3_dll_config *cfg,
+        const wchar_t *filename);
+
 void mu3_hook_config_load(
         struct mu3_hook_config *cfg,
         const wchar_t *filename);
diff --git a/mu3hook/dllmain.c b/mu3hook/dllmain.c
index 08ca989..c7fe361 100644
--- a/mu3hook/dllmain.c
+++ b/mu3hook/dllmain.c
@@ -13,6 +13,7 @@
 
 #include "mu3hook/config.h"
 #include "mu3hook/io4.h"
+#include "mu3hook/mu3-dll.h"
 #include "mu3hook/unity.h"
 
 #include "platform/platform.h"
@@ -62,6 +63,12 @@ static DWORD CALLBACK mu3_pre_startup(void)
         goto fail;
     }
 
+    hr = mu3_dll_init(&mu3_hook_cfg.dll, mu3_hook_mod);
+
+    if (FAILED(hr)) {
+        goto fail;
+    }
+
     hr = mu3_io4_hook_init();
 
     if (FAILED(hr)) {
diff --git a/mu3hook/io4.c b/mu3hook/io4.c
index 5a0b4c0..1fd875a 100644
--- a/mu3hook/io4.c
+++ b/mu3hook/io4.c
@@ -6,7 +6,7 @@
 
 #include "board/io4.h"
 
-#include "mu3io/mu3io.h"
+#include "mu3hook/mu3-dll.h"
 
 #include "util/dprintf.h"
 
@@ -20,13 +20,15 @@ HRESULT mu3_io4_hook_init(void)
 {
     HRESULT hr;
 
+    assert(mu3_dll.init != NULL);
+
     hr = io4_hook_init(&mu3_io4_ops, NULL);
 
     if (FAILED(hr)) {
         return hr;
     }
 
-    return mu3_io_init();
+    return mu3_dll.init();
 }
 
 static HRESULT mu3_io4_poll(void *ctx, struct io4_state *state)
@@ -37,9 +39,14 @@ static HRESULT mu3_io4_poll(void *ctx, struct io4_state *state)
     int16_t lever;
     HRESULT hr;
 
+    assert(mu3_dll.poll != NULL);
+    assert(mu3_dll.get_opbtns != NULL);
+    assert(mu3_dll.get_gamebtns != NULL);
+    assert(mu3_dll.get_lever != NULL);
+
     memset(state, 0, sizeof(*state));
 
-    hr = mu3_io_poll();
+    hr = mu3_dll.poll();
 
     if (FAILED(hr)) {
         return hr;
@@ -50,9 +57,9 @@ static HRESULT mu3_io4_poll(void *ctx, struct io4_state *state)
     right = 0;
     lever = 0;
 
-    mu3_io_get_opbtns(&opbtn);
-    mu3_io_get_gamebtns(&left, &right);
-    mu3_io_get_lever(&lever);
+    mu3_dll.get_opbtns(&opbtn);
+    mu3_dll.get_gamebtns(&left, &right);
+    mu3_dll.get_lever(&lever);
 
     if (opbtn & MU3_IO_OPBTN_TEST) {
         state->buttons[0] |= IO4_BUTTON_TEST;
diff --git a/mu3hook/meson.build b/mu3hook/meson.build
index f777b9d..9931b8b 100644
--- a/mu3hook/meson.build
+++ b/mu3hook/meson.build
@@ -24,6 +24,8 @@ shared_library(
         'dllmain.c',
         'io4.c',
         'io4.h',
+        'mu3-dll.c',
+        'mu3-dll.h',
         'unity.h',
         'unity.c',
     ],
diff --git a/mu3hook/mu3-dll.c b/mu3hook/mu3-dll.c
new file mode 100644
index 0000000..15ed6bb
--- /dev/null
+++ b/mu3hook/mu3-dll.c
@@ -0,0 +1,112 @@
+#include <windows.h>
+
+#include <assert.h>
+#include <stdlib.h>
+
+#include "mu3hook/mu3-dll.h"
+
+#include "util/dll-bind.h"
+#include "util/dprintf.h"
+
+const struct dll_bind_sym mu3_dll_syms[] = {
+    {
+        .sym = "mu3_io_init",
+        .off = offsetof(struct mu3_dll, init),
+    }, {
+        .sym = "mu3_io_poll",
+        .off = offsetof(struct mu3_dll, poll),
+    }, {
+        .sym = "mu3_io_get_opbtns",
+        .off = offsetof(struct mu3_dll, get_opbtns),
+    }, {
+        .sym = "mu3_io_get_gamebtns",
+        .off = offsetof(struct mu3_dll, get_gamebtns),
+    }, {
+        .sym = "mu3_io_get_lever",
+        .off = offsetof(struct mu3_dll, get_lever),
+    }
+};
+
+struct mu3_dll mu3_dll;
+
+// Copypasta DLL binding and diagnostic message boilerplate.
+// Not much of this lends itself to being easily factored out. Also there
+// will be a lot of API-specific branching code here eventually as new API
+// versions get defined, so even though these functions all look the same
+// now this won't remain the case forever.
+
+HRESULT mu3_dll_init(const struct mu3_dll_config *cfg, HINSTANCE self)
+{
+    uint16_t (*get_api_version)(void);
+    const struct dll_bind_sym *sym;
+    HINSTANCE owned;
+    HINSTANCE src;
+    HRESULT hr;
+
+    assert(cfg != NULL);
+    assert(self != NULL);
+
+    if (cfg->path[0] != L'\0') {
+        owned = LoadLibraryW(cfg->path);
+
+        if (owned == NULL) {
+            hr = HRESULT_FROM_WIN32(GetLastError());
+            dprintf("Ongeki IO: Failed to load IO DLL: %x: %S\n",
+                    hr,
+                    cfg->path);
+
+            goto end;
+        }
+
+        dprintf("Ongeki IO: Using custom IO DLL: %S\n", cfg->path);
+        src = owned;
+    } else {
+        owned = NULL;
+        src = self;
+    }
+
+    get_api_version = (void *) GetProcAddress(src, "mu3_io_get_api_version");
+
+    if (get_api_version != NULL) {
+        mu3_dll.api_version = get_api_version();
+    } else {
+        mu3_dll.api_version = 0x0100;
+        dprintf("Custom IO DLL does not expose mu3_io_get_api_version, "
+                "assuming API version 1.0.\n"
+                "Please ask the developer to update their DLL.\n");
+    }
+
+    if (mu3_dll.api_version >= 0x0200) {
+        hr = E_NOTIMPL;
+        dprintf("Ongeki IO: Custom IO DLL implements an unsupported "
+                "API version (%#04x). Please update Segatools.\n",
+                mu3_dll.api_version);
+
+        goto end;
+    }
+
+    sym = mu3_dll_syms;
+    hr = dll_bind(&mu3_dll, src, &sym, _countof(mu3_dll_syms));
+
+    if (FAILED(hr)) {
+        if (src != self) {
+            dprintf("Ongeki IO: Custom IO DLL does not provide function "
+                    "\"%s\". Please contact your IO DLL's developer for "
+                    "further assistance.\n",
+                    sym->sym);
+
+            goto end;
+        } else {
+            dprintf("Internal error: could not reflect \"%s\"\n", sym->sym);
+        }
+    }
+
+    owned = NULL;
+
+end:
+    if (owned != NULL) {
+        FreeLibrary(owned);
+    }
+
+    return hr;
+}
diff --git a/mu3hook/mu3-dll.h b/mu3hook/mu3-dll.h
new file mode 100644
index 0000000..41f280f
--- /dev/null
+++ b/mu3hook/mu3-dll.h
@@ -0,0 +1,22 @@
+#pragma once
+
+#include <windows.h>
+
+#include "mu3io/mu3io.h"
+
+struct mu3_dll {
+    uint16_t api_version;
+    HRESULT (*init)(void);
+    HRESULT (*poll)(void);
+    void (*get_opbtns)(uint8_t *opbtn);
+    void (*get_gamebtns)(uint8_t *left, uint8_t *right);
+    void (*get_lever)(int16_t *pos);
+};
+
+struct mu3_dll_config {
+    wchar_t path[MAX_PATH];
+};
+
+extern struct mu3_dll mu3_dll;
+
+HRESULT mu3_dll_init(const struct mu3_dll_config *cfg, HINSTANCE self);
diff --git a/mu3hook/mu3hook.def b/mu3hook/mu3hook.def
index c819437..b3a1840 100644
--- a/mu3hook/mu3hook.def
+++ b/mu3hook/mu3hook.def
@@ -12,3 +12,8 @@ EXPORTS
     amDllVideoGetVBiosVersion @4
     amDllVideoOpen @1
     amDllVideoSetResolution @3
+    mu3_io_get_gamebtns
+    mu3_io_get_lever
+    mu3_io_get_opbtns
+    mu3_io_init
+    mu3_io_poll