diff --git a/src/sys/ags.cpp b/src/sys/ags.cpp
index b9afe3c..490c5cc 100644
--- a/src/sys/ags.cpp
+++ b/src/sys/ags.cpp
@@ -62,7 +62,7 @@ SDL_Texture* create_scanline_texture(SDL_Renderer* renderer, int width, int heig
 AGS::AGS(const Config& config, const GameId& game_id) : game_id(game_id), dirty(false)
 {
 	// 画面サイズ
-	if (game_id.crc32_a == CRC32_GAKUEN || game_id.crc32_a == CRC32_GAKUEN_ENG) {
+	if (game_id.is_gakuen()) {
 		window_width = 582;
 		screen_width = 512;
 		window_height = screen_height = 424;
@@ -619,7 +619,7 @@ void AGS::save_screenshot(const char* path)
 int AGS::calculate_menu_max(int window) {
 	if (game_id.crc32_a == CRC32_INTRUDER)
 		return 6;
-	if (game_id.crc32_a == CRC32_GAKUEN || game_id.crc32_a == CRC32_GAKUEN_ENG)
+	if (game_id.is_gakuen())
 		return (menu_w[window - 1].ey - menu_w[window - 1].sy) / (menu_font_size + 4);
 	return 11;
 }
diff --git a/src/sys/ags_pms.cpp b/src/sys/ags_pms.cpp
index 99b0046..4d4e5f8 100644
--- a/src/sys/ags_pms.cpp
+++ b/src/sys/ags_pms.cpp
@@ -41,11 +41,7 @@ void AGS::load_pms(uint8* data, int page, int transparent)
 				tmp_palette[i * 16 + j] = SETPALETTE256(r, g, b);
 			}
 		}
-		if (game_id.crc32_a == CRC32_RANCE41 ||
-		    game_id.crc32_a == CRC32_RANCE41_ENG ||
-		    game_id.crc32_a == CRC32_RANCE42 ||
-		    game_id.crc32_a == CRC32_RANCE42_ENG ||
-		    game_id.crc32_a == CRC32_HASHIRIONNA2) {
+		if (game_id.is_rance4x() || game_id.crc32_a == CRC32_HASHIRIONNA2) {
 			// 上下16色は取得しない
 			for(int i = 1; i < 15; i++) {
 				for(int j = 0; j < 16; j++) {
@@ -77,11 +73,7 @@ void AGS::load_pms(uint8* data, int page, int transparent)
 	// パレット展開
 	if (game_id.sys_ver == 3) {
 		if ((extract_palette && extract_palette_cg[page]) || game_id.crc32_a == CRC32_FUNNYBEE_CD) {
-			if (game_id.crc32_a == CRC32_RANCE41 ||
-			    game_id.crc32_a == CRC32_RANCE41_ENG ||
-			    game_id.crc32_a == CRC32_RANCE42 ||
-			    game_id.crc32_a == CRC32_RANCE42_ENG ||
-			    game_id.crc32_a == CRC32_HASHIRIONNA2) {
+			if (game_id.is_rance4x() || game_id.crc32_a == CRC32_HASHIRIONNA2) {
 				// 上下16色は展開しない
 				for(int i = 1; i < 15; i++) {
 					for(int j = 0; j < 16; j++) {
diff --git a/src/sys/ags_vsp.cpp b/src/sys/ags_vsp.cpp
index a3f4200..427c85c 100644
--- a/src/sys/ags_vsp.cpp
+++ b/src/sys/ags_vsp.cpp
@@ -143,7 +143,7 @@ void AGS::load_vsp(uint8* data, int page, int transparent)
 
 				uint32* dest;
 				// Gakuen Senki uses exact sx values rather than 8x.
-				if (game_id.crc32_a == CRC32_GAKUEN || game_id.crc32_a == CRC32_GAKUEN_ENG)
+				if (game_id.is_gakuen())
 					dest = &vram[dest_screen][y + sy][(x * 8) + sx];
 				else
 					dest = &vram[dest_screen][y + sy][(x + sx) * 8];
@@ -165,7 +165,7 @@ void AGS::load_vsp(uint8* data, int page, int transparent)
 
 	// 画面更新
 	if(dest_screen == 0 && extract_cg) {
-		if (game_id.crc32_a == CRC32_GAKUEN || game_id.crc32_a == CRC32_GAKUEN_ENG) {
+		if (game_id.is_gakuen()) {
 			// Gakuen Senki's images were converted to VSP for the modern port, but don't always adhere to VSP's width restrictions, which demand
 			// every image width be a factor of 8. Thankfully, the exceptions are designed to fit into specific parts of the GUI, and so have
 			// consistent widths for each output position.
diff --git a/src/sys/dri.cpp b/src/sys/dri.cpp
index 6923749..248dfc3 100644
--- a/src/sys/dri.cpp
+++ b/src/sys/dri.cpp
@@ -57,12 +57,12 @@ std::vector<uint8> Dri::load(int page)
 }
 
 // static
-std::vector<uint8> Dri::load_mda(uint32_t crc32_a, uint32_t crc32_b, int page)
+std::vector<uint8> Dri::load_mda(const GameId& game_id, int page)
 {
 	// データ取得
 	const char* name = NULL;
 
-	switch(crc32_a) {
+	switch (game_id.crc32_a) {
 		case CRC32_BUNKASAI:		// あぶない文化祭前夜
 			name = "AMUS_AB.MDA";
 			break;
@@ -206,7 +206,7 @@ std::vector<uint8> Dri::load_mda(uint32_t crc32_a, uint32_t crc32_b, int page)
 	// AMUS.MDA以外にリンクされている場合はリソースを開き直す
 	if(disk_index == 2) {
 		SDL_RWclose(rw);
-		switch(crc32_b) {
+		switch (game_id.crc32_b) {
 			case CRC32_DPS_SG_FAHREN:	// D.P.S. SG - Fahren Fliegen
 				name = "BMUS_FAH";
 				break;
@@ -255,7 +255,7 @@ std::vector<uint8> Dri::load_mda(uint32_t crc32_a, uint32_t crc32_b, int page)
 		}
 	} else if(disk_index == 3) {
 		SDL_RWclose(rw);
-		switch(crc32_a) {
+		switch (game_id.crc32_a) {
 			case CRC32_TOUSHIN_HINT:	// 闘神都市 ヒントディスク
 				name = "CMUS_T1";
 				break;
diff --git a/src/sys/dri.h b/src/sys/dri.h
index b60c461..b40579d 100644
--- a/src/sys/dri.h
+++ b/src/sys/dri.h
@@ -11,12 +11,14 @@
 #include <stdint.h>
 #include <vector>
 
+struct GameId;
+
 class Dri {
 public:
 	void open(const char* file_name);
 	std::vector<uint8_t> load(int page);
 
-	static std::vector<uint8_t> load_mda(uint32_t crc32_a, uint32_t crc32_b, int page);
+	static std::vector<uint8_t> load_mda(const GameId& game_id, int page);
 
 private:
 	std::string fname;
diff --git a/src/sys/game_id.h b/src/sys/game_id.h
index 7baa291..746f01d 100644
--- a/src/sys/game_id.h
+++ b/src/sys/game_id.h
@@ -91,6 +91,16 @@ struct GameId {
 	const char* encoding;
 
 	explicit GameId(const Config& config);
+	bool is_gakuen() const {
+		return crc32_a == CRC32_GAKUEN || crc32_a == CRC32_GAKUEN_ENG;
+	}
+	bool is_system1_dps() const {
+		return crc32_a == CRC32_DPS || crc32_a == CRC32_DPS_SG || crc32_a == CRC32_DPS_SG2 || crc32_a == CRC32_DPS_SG3;
+	}
+	bool is_rance4x() const {
+		return crc32_a == CRC32_RANCE41 || crc32_a == CRC32_RANCE42 ||
+			crc32_a == CRC32_RANCE41_ENG || crc32_a == CRC32_RANCE42_ENG;
+	}
 };
 
 #endif  // _GAMEID_H_
diff --git a/src/sys/mako_midi.cpp b/src/sys/mako_midi.cpp
index 003d600..2bd0cc1 100644
--- a/src/sys/mako_midi.cpp
+++ b/src/sys/mako_midi.cpp
@@ -94,7 +94,7 @@ void stop_midi()
 class Playback {
 public:
 	static std::unique_ptr<Playback> create(const GameId& game_id, Dri& amus, Dri& mda, int page, int loop, int seq);
-	Playback(uint32_t crc32_a, int loop, int seq) : crc32_a(crc32_a), loop_(loop), seq_(seq) {}
+	Playback(const GameId& game_id, int loop, int seq) : game_id(game_id), loop_(loop), seq_(seq) {}
 	bool load_mml(const std::vector<uint8_t>& data);
 	void load_mda(const std::vector<uint8_t>& data);
 	void start_midi();
@@ -102,7 +102,7 @@ public:
 	int seq() const { return seq_; }
 
 private:
-	uint32_t crc32_a;
+	const GameId& game_id;
 	int loop_;
 	int seq_;
 
@@ -320,7 +320,7 @@ bool Playback::play_midi(SDL_atomic_t* current_loop, SDL_atomic_t* current_mark)
 					send_3bytes(0xb0 + play[i].channel, 0x0a, play[i].pan);
 				}
 				else if(d0 == 0xec) {
-					if(!(crc32_a == CRC32_DPS || crc32_a == CRC32_DPS_SG || crc32_a == CRC32_DPS_SG2 || crc32_a == CRC32_DPS_SG3))
+					if (!game_id.is_system1_dps())
 						mute_flag = true;
 				}
 				else if(d0 == 0xf5) {
@@ -381,7 +381,7 @@ bool Playback::play_midi(SDL_atomic_t* current_loop, SDL_atomic_t* current_mark)
 //static
 std::unique_ptr<Playback> Playback::create(const GameId& game_id, Dri& amus, Dri& mda, int page, int loop, int seq)
 {
-	auto playback = std::make_unique<Playback>(game_id.crc32_a, loop, seq);
+	auto playback = std::make_unique<Playback>(game_id, loop, seq);
 
 	std::vector<uint8_t> data = amus.load(page);
 	if (data.empty())
@@ -392,7 +392,7 @@ std::unique_ptr<Playback> Playback::create(const GameId& game_id, Dri& amus, Dri
 	// Load MDA
 	data = mda.load(page);
 	if (data.empty())
-		data = Dri::load_mda(game_id.crc32_a, game_id.crc32_b, page);
+		data = Dri::load_mda(game_id, page);
 	playback->load_mda(data);
 
 	return playback;
diff --git a/src/sys/nact.cpp b/src/sys/nact.cpp
index 0f6c5c5..e08fe78 100644
--- a/src/sys/nact.cpp
+++ b/src/sys/nact.cpp
@@ -321,7 +321,7 @@ void NACT::cmd_set_menu()
 		ags->menu_dest_y += 2;
 		ags->draw_menu = true;
 
-		if (game_id.crc32_a == CRC32_GAKUEN || game_id.crc32_a == CRC32_GAKUEN_ENG)
+		if (game_id.is_gakuen())
 			menu_window = 2;
 
 		output_console("\n$%x,", menu_addr[menu_index - 1]);
@@ -337,7 +337,7 @@ void NACT::cmd_open_menu()
 		return;
 	}
 
-	if (game_id.crc32_a == CRC32_DPS || game_id.crc32_a == CRC32_DPS_SG || game_id.crc32_a == CRC32_DPS_SG2 || game_id.crc32_a == CRC32_DPS_SG3) {
+	if (game_id.is_system1_dps()) {
 		if (!text_refresh) {
 			cmd_a();
 		}
@@ -421,7 +421,7 @@ void NACT::cmd_a()
 	// ウィンドウ更新
 	ags->clear_text_window(text_window, true);
 
-	if (game_id.crc32_a == CRC32_DPS || game_id.crc32_a == CRC32_DPS_SG || game_id.crc32_a == CRC32_DPS_SG2 || game_id.crc32_a == CRC32_DPS_SG3) {
+	if (game_id.is_system1_dps()) {
 		text_refresh = true;
 	}
 }
@@ -490,7 +490,7 @@ void NACT::message(uint8_t first_byte)
 
 	ags->draw_text(buf, text_wait_enb);
 
-	if (game_id.crc32_a == CRC32_DPS || game_id.crc32_a == CRC32_DPS_SG || game_id.crc32_a == CRC32_DPS_SG2 || game_id.crc32_a == CRC32_DPS_SG3) {
+	if (game_id.is_system1_dps()) {
 		if(!ags->draw_menu) {
 			text_refresh = false;
 		}
diff --git a/src/sys/nact.h b/src/sys/nact.h
index a6cbe25..899a78d 100644
--- a/src/sys/nact.h
+++ b/src/sys/nact.h
@@ -168,9 +168,6 @@ protected:
 	// DPS
 	bool text_refresh;
 
-	// GAKUEN
-	bool enable_graphics = true;
-
 	bool column = true;		// 座標モード
 	bool wait_keydown = true;	// ウェイト時のキー受付
 	int text_wait_time = 100;	// テキスト表示のウェイト
@@ -291,6 +288,9 @@ private:
 	int paint_x;
 	int paint_y;
 	int map_page;
+
+	// GAKUEN
+	bool enable_graphics = true;
 };
 
 class NACT_Sys2 final : public NACT {
diff --git a/src/sys/nact_sys1.cpp b/src/sys/nact_sys1.cpp
index 50055bc..385fab0 100644
--- a/src/sys/nact_sys1.cpp
+++ b/src/sys/nact_sys1.cpp
@@ -224,7 +224,7 @@ void NACT_Sys1::cmd_open_verb()
 	// 表示する動詞のチェック
 	int chk[MAX_VERB], page = 0, cnt = 0;
 	
-	if (game_id.crc32_a == CRC32_GAKUEN || game_id.crc32_a == CRC32_GAKUEN_ENG)
+	if (game_id.is_gakuen())
 		menu_window = 1;
 	int menu_max = ags->calculate_menu_max(menu_window);
 
@@ -431,7 +431,7 @@ void NACT_Sys1::cmd_g()
 
 	if (game_id.crc32_a == CRC32_INTRUDER) {
 		page = (page == 97) ? 96 : (page == 98) ? 97 : page;
-	} else if (game_id.crc32_a == CRC32_GAKUEN || game_id.crc32_a == CRC32_GAKUEN_ENG) {
+	} else if (game_id.is_gakuen()) {
 		page = (page == 3) ? 94 : page;
 	}
 
@@ -620,7 +620,7 @@ void NACT_Sys1::cmd_y()
 				quit(NACT_HALT);
 				break;
 		}
-	} else if (game_id.crc32_a == CRC32_GAKUEN || game_id.crc32_a == CRC32_GAKUEN_ENG) {
+	} else if (game_id.is_gakuen()) {
 		switch (cmd) {
 			case 1:
 				RND = (param == 0 || param == 1) ? 0 : random(param);
@@ -688,7 +688,7 @@ void NACT_Sys1::cmd_y()
 					for(int i = 39; i <= 48; i++) {
 						var[i] = 0;
 					}
-				} else if (game_id.crc32_a == CRC32_DPS || game_id.crc32_a == CRC32_DPS_SG || game_id.crc32_a == CRC32_DPS_SG2 || game_id.crc32_a == CRC32_DPS_SG3) {
+				} else if (game_id.is_system1_dps()) {
 					for(int i = 0; i <= 20; i++) {
 						var[i] = 0;
 					}
@@ -705,7 +705,7 @@ void NACT_Sys1::cmd_y()
 				RND = (param == 0 || param == 1) ? 0 : random(param);
 				break;
 			case 7:
-				if (game_id.crc32_a == CRC32_DPS || game_id.crc32_a == CRC32_DPS_SG || game_id.crc32_a == CRC32_DPS_SG2 || game_id.crc32_a == CRC32_DPS_SG3) {
+				if (game_id.is_system1_dps()) {
 					if(param == 1) {
 						ags->box_fill(0, 40, 8, 598, 270, 0);
 					}
@@ -749,7 +749,7 @@ void NACT_Sys1::cmd_y()
 				RND = 0;
 				break;
 			case 255:
-				if (game_id.crc32_a == CRC32_DPS || game_id.crc32_a == CRC32_DPS_SG || game_id.crc32_a == CRC32_DPS_SG2 || game_id.crc32_a == CRC32_DPS_SG3) {
+				if (game_id.is_system1_dps()) {
 					quit(0);
 				} else {
 					quit(NACT_HALT);
diff --git a/src/sys/nact_sys3.cpp b/src/sys/nact_sys3.cpp
index 50494cb..bde4eb1 100644
--- a/src/sys/nact_sys3.cpp
+++ b/src/sys/nact_sys3.cpp
@@ -608,8 +608,7 @@ void NACT_Sys3::cmd_u()
 
 	output_console("\nU %d,%d:", page, transparent);
 
-	if (game_id.crc32_a == CRC32_RANCE41 || game_id.crc32_a == CRC32_RANCE41_ENG ||
-	    game_id.crc32_a == CRC32_RANCE42 || game_id.crc32_a == CRC32_RANCE42_ENG) {
+	if (game_id.is_rance4x()) {
 		transparent = (transparent == 28) ? 12 : transparent;
 	}
 	ags->load_cg(page, transparent);