diff --git a/packages/three-vrm-core/src/expressions/VRMExpression.ts b/packages/three-vrm-core/src/expressions/VRMExpression.ts
index 509d6faf2..4dfbd5706 100644
--- a/packages/three-vrm-core/src/expressions/VRMExpression.ts
+++ b/packages/three-vrm-core/src/expressions/VRMExpression.ts
@@ -1,6 +1,7 @@
 import * as THREE from 'three';
 import { VRMExpressionBind } from './VRMExpressionBind';
 import type { VRMExpressionOverrideType } from './VRMExpressionOverrideType';
+import type { VRMExpressionManager } from './VRMExpressionManager';
 
 // animationMixer の監視対象は、Scene の中に入っている必要がある。
 // そのため、表示オブジェクトではないけれど、Object3D を継承して Scene に投入できるようにする。
@@ -13,6 +14,10 @@ export class VRMExpression extends THREE.Object3D {
 
   /**
    * The current weight of the expression.
+   *
+   * You usually want to set the weight via {@link VRMExpressionManager.setValue}.
+   *
+   * It might also be controlled by the Three.js animation system.
    */
   public weight = 0.0;
 
@@ -46,9 +51,9 @@ export class VRMExpression extends THREE.Object3D {
    */
   public get overrideBlinkAmount(): number {
     if (this.overrideBlink === 'block') {
-      return 0.0 < this.weight ? 1.0 : 0.0;
+      return 0.0 < this.outputWeight ? 1.0 : 0.0;
     } else if (this.overrideBlink === 'blend') {
-      return this.weight;
+      return this.outputWeight;
     } else {
       return 0.0;
     }
@@ -60,9 +65,9 @@ export class VRMExpression extends THREE.Object3D {
    */
   public get overrideLookAtAmount(): number {
     if (this.overrideLookAt === 'block') {
-      return 0.0 < this.weight ? 1.0 : 0.0;
+      return 0.0 < this.outputWeight ? 1.0 : 0.0;
     } else if (this.overrideLookAt === 'blend') {
-      return this.weight;
+      return this.outputWeight;
     } else {
       return 0.0;
     }
@@ -74,14 +79,25 @@ export class VRMExpression extends THREE.Object3D {
    */
   public get overrideMouthAmount(): number {
     if (this.overrideMouth === 'block') {
-      return 0.0 < this.weight ? 1.0 : 0.0;
+      return 0.0 < this.outputWeight ? 1.0 : 0.0;
     } else if (this.overrideMouth === 'blend') {
-      return this.weight;
+      return this.outputWeight;
     } else {
       return 0.0;
     }
   }
 
+  /**
+   * An output weight of this expression, considering the {@link isBinary}.
+   */
+  public get outputWeight(): number {
+    if (this.isBinary) {
+      return this.weight > 0.5 ? 1.0 : 0.0;
+    }
+
+    return this.weight;
+  }
+
   constructor(expressionName: string) {
     super();
 
@@ -112,9 +128,14 @@ export class VRMExpression extends THREE.Object3D {
      */
     multiplier?: number;
   }): void {
-    let actualWeight = this.isBinary ? (this.weight <= 0.5 ? 0.0 : 1.0) : this.weight;
+    let actualWeight = this.outputWeight;
     actualWeight *= options?.multiplier ?? 1.0;
 
+    // if the expression is binary, the override value must be also treated as binary
+    if (this.isBinary && actualWeight < 1.0) {
+      actualWeight = 0.0;
+    }
+
     this._binds.forEach((bind) => bind.applyWeight(actualWeight));
   }
 
diff --git a/packages/three-vrm-core/src/expressions/tests/VRMExpression.test.ts b/packages/three-vrm-core/src/expressions/tests/VRMExpression.test.ts
new file mode 100644
index 000000000..1b4af5a04
--- /dev/null
+++ b/packages/three-vrm-core/src/expressions/tests/VRMExpression.test.ts
@@ -0,0 +1,190 @@
+import { VRMExpression } from '../VRMExpression';
+import { VRMExpressionBind } from '../VRMExpressionBind';
+
+class VRMExpressionMockBind implements VRMExpressionBind {
+  public weight = 0.0;
+
+  public applyWeight(weight: number): void {
+    this.weight += weight;
+  }
+
+  public clearAppliedWeight(): void {
+    this.weight = 0.0;
+  }
+}
+
+describe('VRMExpression', () => {
+  let expression: VRMExpression;
+
+  beforeEach(() => {
+    expression = new VRMExpression('aa');
+  });
+
+  describe('outputWeight', () => {
+    it('returns the weight if the expression is not binary', () => {
+      expression.weight = 0.64;
+      expect(expression.outputWeight).toBe(0.64);
+    });
+
+    it('returns 0.0 if the expression is binary and the weight is less than 0.5', () => {
+      expression.isBinary = true;
+      expression.weight = 0.3;
+      expect(expression.outputWeight).toBe(0.0);
+    });
+
+    it('returns 1.0 if the expression is binary and the weight is more than 0.5', () => {
+      expression.isBinary = true;
+      expression.weight = 0.7;
+      expect(expression.outputWeight).toBe(1.0);
+    });
+
+    it('returns 0.0 if the expression is binary and the weight is exactly 0.5', () => {
+      expression.isBinary = true;
+      expression.weight = 0.5;
+      expect(expression.outputWeight).toBe(0.0);
+    });
+  });
+
+  describe('overrideBlinkAmount', () => {
+    it('returns 0.0 when the overrideBlink is none', () => {
+      expression.overrideBlink = 'none';
+      expression.weight = 0.75;
+      expect(expression.overrideBlinkAmount).toBe(0.0);
+    });
+
+    it('returns the override amount when the overrideBlink is blend', () => {
+      expression.overrideBlink = 'blend';
+      expression.weight = 0.75;
+      expect(expression.overrideBlinkAmount).toBe(0.75);
+    });
+
+    it('returns 1.0 when the overrideBlink is block and the weight is not zero', () => {
+      expression.overrideBlink = 'block';
+      expression.weight = 0.1;
+      expect(expression.overrideBlinkAmount).toBe(1.0);
+    });
+
+    it('returns 0.0 when the overrideBlink is block and the weight is exactly zero', () => {
+      expression.overrideBlink = 'block';
+      expression.weight = 0.0;
+      expect(expression.overrideBlinkAmount).toBe(0.0);
+    });
+
+    it('returns 0.0 when the expression is binary, the overrideBlink is blend, and the weight is less than 0.5', () => {
+      expression.overrideBlink = 'blend';
+      expression.isBinary = true;
+      expression.weight = 0.3;
+      expect(expression.overrideBlinkAmount).toBe(0.0);
+    });
+
+    it('returns 1.0 when the expression is binary, the overrideBlink is blend, and the weight is more than 0.5', () => {
+      expression.overrideBlink = 'blend';
+      expression.isBinary = true;
+      expression.weight = 0.7;
+      expect(expression.overrideBlinkAmount).toBe(1.0);
+    });
+
+    it('returns 0.0 when the expression is binary, the overrideBlink is block, and the weight is less than 0.5', () => {
+      expression.overrideBlink = 'block';
+      expression.isBinary = true;
+      expression.weight = 0.3;
+      expect(expression.overrideBlinkAmount).toBe(0.0);
+    });
+
+    it('returns 1.0 when the expression is binary, the overrideBlink is block, and the weight is more than 0.5', () => {
+      expression.overrideBlink = 'block';
+      expression.isBinary = true;
+      expression.weight = 0.7;
+      expect(expression.overrideBlinkAmount).toBe(1.0);
+    });
+  });
+
+  describe('applyWeight', () => {
+    it('applies the weight to the binds', () => {
+      const bind1 = new VRMExpressionMockBind();
+      const bind2 = new VRMExpressionMockBind();
+      expression.addBind(bind1);
+      expression.addBind(bind2);
+
+      expression.weight = 0.64;
+      expression.applyWeight();
+
+      expect(bind1.weight).toBe(0.64);
+      expect(bind2.weight).toBe(0.64);
+    });
+
+    it('applies the 0.0 if the expression is binary and the weight is less than 0.5', () => {
+      expression.isBinary = true;
+
+      const bind = new VRMExpressionMockBind();
+      expression.addBind(bind);
+
+      expression.weight = 0.3;
+      expression.applyWeight();
+
+      expect(bind.weight).toBe(0.0);
+    });
+
+    it('applies the 1.0 if the expression is binary and the weight is more than 0.5', () => {
+      expression.isBinary = true;
+
+      const bind = new VRMExpressionMockBind();
+      expression.addBind(bind);
+
+      expression.weight = 0.7;
+      expression.applyWeight();
+
+      expect(bind.weight).toBe(1.0);
+    });
+
+    it('applies the 0.0 if the expression is binary and the weight is exactly 0.5', () => {
+      expression.isBinary = true;
+
+      const bind = new VRMExpressionMockBind();
+      expression.addBind(bind);
+
+      expression.weight = 0.5;
+      expression.applyWeight();
+
+      expect(bind.weight).toBe(0.0);
+    });
+
+    it('applies the weight with the override multiplier', () => {
+      const bind = new VRMExpressionMockBind();
+      expression.addBind(bind);
+
+      expression.weight = 0.75;
+      expression.applyWeight({ multiplier: 0.5 });
+
+      expect(bind.weight).toBe(0.375);
+    });
+
+    it('applies the 0.0 if the expression is binary and the override multiplier is less than 1.0', () => {
+      expression.isBinary = true;
+
+      const bind = new VRMExpressionMockBind();
+      expression.addBind(bind);
+
+      expression.weight = 0.7;
+      expression.applyWeight({ multiplier: 0.99 });
+
+      expect(bind.weight).toBe(0.0);
+    });
+  });
+
+  describe('clearAppliedWeight', () => {
+    it('clears the applied weight from the binds', () => {
+      const bind1 = new VRMExpressionMockBind();
+      const bind2 = new VRMExpressionMockBind();
+      bind1.applyWeight(0.82);
+      bind2.applyWeight(0.48);
+      expression.addBind(bind1);
+      expression.addBind(bind2);
+
+      expression.clearAppliedWeight();
+
+      expect(bind1.weight).toBe(0.0);
+      expect(bind2.weight).toBe(0.0);
+    });
+  });
+});