diff --git a/packages-user/data-state/src/core.ts b/packages-user/data-state/src/core.ts
index 9d9845f..8d940c9 100644
--- a/packages-user/data-state/src/core.ts
+++ b/packages-user/data-state/src/core.ts
@@ -344,6 +344,7 @@ export class CoreState implements ICoreState {
             state.setLayerAlias(bg, 'bg');
             state.setLayerAlias(bg2, 'bg2');
             state.setLayerAlias(event, 'event');
+            state.setEventLayer(event);
             state.setLayerAlias(fg, 'fg');
             state.setLayerAlias(fg2, 'fg2');
             state.setActiveStatus(false);
diff --git a/packages-user/data-state/src/coreEventLayer.test.ts b/packages-user/data-state/src/coreEventLayer.test.ts
new file mode 100644
index 0000000..bafc255
--- /dev/null
+++ b/packages-user/data-state/src/coreEventLayer.test.ts
@@ -0,0 +1,187 @@
+import { beforeAll, describe, expect, it, vi } from 'vitest';
+
+interface TestModules {
+    CoreState: typeof import('./core').CoreState;
+}
+
+interface FakeLayer {
+    zIndex: number;
+    alias: string | null;
+    map: Uint32Array | null;
+    setZIndex(zIndex: number): void;
+    setMapRef(map: Uint32Array): void;
+}
+
+interface FakeGameMap {
+    readonly layers: FakeLayer[];
+    eventLayer: FakeLayer | null;
+    addLayer(): FakeLayer;
+    setLayerAlias(layer: FakeLayer, alias: string): void;
+    setEventLayer(layer: FakeLayer | null): void;
+    setActiveStatus(active: boolean): void;
+}
+
+interface FakeMapState {
+    readonly createdMaps: Map<string, FakeGameMap>;
+    comparedWith: Map<string, Map<number, Uint32Array>> | null;
+    createMap(id: string, width: number, height: number): FakeGameMap;
+    compareWith(reference: Map<string, Map<number, Uint32Array>>): void;
+}
+
+interface LegacyFloor {
+    readonly width: number;
+    readonly height: number;
+    readonly bgmap: number[][];
+    readonly bg2map: number[][];
+    readonly map: number[][];
+    readonly fgmap: number[][];
+    readonly fg2map: number[][];
+}
+
+interface CoreInitializer {
+    maps: FakeMapState;
+    initMapState(floors: string[], data: Record<string, LegacyFloor>): void;
+}
+
+vi.mock('./enemy', () => ({
+    CommonAuraConverter: class {},
+    EnemyLegacyBridge: class {},
+    GuardAuraConverter: class {},
+    MainDamageCalculator: class {},
+    MainEnemyComparer: class {},
+    MainEnemyFinalEffect: class {},
+    MainMapDamageConverter: class {},
+    MainMapDamageReducer: class {},
+    registerSpecials: vi.fn()
+}));
+
+vi.mock('./legacy', () => ({
+    ItemLegacyBridge: class {},
+    TileLegacyBridge: class {}
+}));
+
+let modules: TestModules;
+
+beforeAll(async () => {
+    vi.stubGlobal('main', { replayChecking: true });
+    vi.stubGlobal('location', { origin: 'http://localhost' });
+    const coreModule = await import('./core');
+    modules = { CoreState: coreModule.CoreState };
+});
+
+function createFakeMapState(): FakeMapState {
+    const createdMaps = new Map<string, FakeGameMap>();
+    return {
+        createdMaps,
+        comparedWith: null,
+        createMap(id, width, height) {
+            const map: FakeGameMap = {
+                layers: [],
+                eventLayer: null,
+                addLayer() {
+                    const layer: FakeLayer = {
+                        zIndex: 0,
+                        alias: null,
+                        map: new Uint32Array(width * height),
+                        setZIndex(zIndex) {
+                            layer.zIndex = zIndex;
+                        },
+                        setMapRef(map) {
+                            layer.map = map;
+                        }
+                    };
+                    map.layers.push(layer);
+                    return layer;
+                },
+                setLayerAlias(layer, alias) {
+                    layer.alias = alias;
+                },
+                setEventLayer(layer) {
+                    map.eventLayer = layer;
+                },
+                setActiveStatus() {}
+            };
+            createdMaps.set(id, map);
+            return map;
+        },
+        compareWith(reference) {
+            this.comparedWith = reference;
+        }
+    };
+}
+
+function createFloor(offset: number): LegacyFloor {
+    return {
+        width: 2,
+        height: 1,
+        bgmap: [[offset + 1, offset + 2]],
+        bg2map: [[offset + 3, offset + 4]],
+        map: [[offset + 5, offset + 6]],
+        fgmap: [[offset + 7, offset + 8]],
+        fg2map: [[offset + 9, offset + 10]]
+    };
+}
+
+describe('CoreState legacy event-layer initialization', () => {
+    it('selects the event alias layer without changing map assembly', () => {
+        const maps = createFakeMapState();
+        const initializer = Object.create(
+            modules.CoreState.prototype
+        ) as CoreInitializer;
+        initializer.maps = maps;
+
+        const floors = ['F1', 'F2'];
+        const data = { F1: createFloor(0), F2: createFloor(10) };
+        initializer.initMapState(floors, data);
+
+        expect([...maps.createdMaps.keys()]).toEqual(floors);
+        for (const id of floors) {
+            const map = maps.createdMaps.get(id)!;
+            expect(map.layers.map(layer => layer.alias)).toEqual([
+                'bg',
+                'bg2',
+                'event',
+                'fg',
+                'fg2'
+            ]);
+            expect(map.layers.map(layer => layer.zIndex)).toEqual([
+                0, 10, 20, 30, 40
+            ]);
+            expect(map.eventLayer).toBe(map.layers[2]);
+        }
+
+        expect(
+            maps.createdMaps.get('F1')!.layers.map(layer => layer.map)
+        ).toEqual([
+            new Uint32Array([1, 2]),
+            new Uint32Array([3, 4]),
+            new Uint32Array([5, 6]),
+            new Uint32Array([7, 8]),
+            new Uint32Array([9, 10])
+        ]);
+        expect(maps.comparedWith).toEqual(
+            new Map([
+                [
+                    'F1',
+                    new Map([
+                        [0, new Uint32Array([1, 2])],
+                        [10, new Uint32Array([3, 4])],
+                        [20, new Uint32Array([5, 6])],
+                        [30, new Uint32Array([7, 8])],
+                        [40, new Uint32Array([9, 10])]
+                    ])
+                ],
+                [
+                    'F2',
+                    new Map([
+                        [0, new Uint32Array([11, 12])],
+                        [10, new Uint32Array([13, 14])],
+                        [20, new Uint32Array([15, 16])],
+                        [30, new Uint32Array([17, 18])],
+                        [40, new Uint32Array([19, 20])]
+                    ])
+                ]
+            ])
+        );
+    });
+});