diff --git a/include/reign.h b/include/reign.h
index 82d3800..4f5cfd7 100644
--- a/include/reign.h
+++ b/include/reign.h
@@ -199,6 +199,7 @@ struct RE_instance {
 	float pitch, roll, yaw;  // in degrees
 	vec3 scale;
 	float alpha;
+	float grayscale_rate;
 	bool draw;
 	bool draw_edge;
 	bool draw_shadow;
diff --git a/shaders/reign.f.glsl b/shaders/reign.f.glsl
index e0f2fad..5f26117 100644
--- a/shaders/reign.f.glsl
+++ b/shaders/reign.f.glsl
@@ -108,6 +108,7 @@ in vec3 specular_dir;
 uniform vec4 tonemap_param;   // (ExposureBias, WhitePoint, A, B)
 uniform vec4 tonemap_param2;  // (C, D, E, F)
 uniform bool nolighting;
+uniform float grayscale_rate;
 
 vec3 hable(vec3 v)
 {
@@ -239,6 +240,9 @@ void main() {
 #if ENGINE == SEAL_ENGINE
 	if (!nolighting)
 		frag_rgb = tone_map(frag_rgb);
+
+	if (grayscale_rate != 0.0)
+		frag_rgb = mix(frag_rgb, vec3(dot(frag_rgb, vec3(0.299, 0.587, 0.114))), grayscale_rate);
 #endif
 
 	// Alpha mapping
diff --git a/src/3d/3d_internal.h b/src/3d/3d_internal.h
index 539f22d..f3ae67e 100644
--- a/src/3d/3d_internal.h
+++ b/src/3d/3d_internal.h
@@ -195,6 +195,7 @@ struct RE_renderer {
 	GLint tonemap_param;
 	GLint tonemap_param2;
 	GLint nolighting;
+	GLint grayscale_rate;
 	GLint alpha_mode;
 	GLint alpha_texture;
 	GLint uv_scroll;
diff --git a/src/3d/renderer.c b/src/3d/renderer.c
index 635aad8..7f8a269 100644
--- a/src/3d/renderer.c
+++ b/src/3d/renderer.c
@@ -283,6 +283,7 @@ struct RE_renderer *RE_renderer_new(void)
 	r->tonemap_param = glGetUniformLocation(r->program, "tonemap_param");
 	r->tonemap_param2 = glGetUniformLocation(r->program, "tonemap_param2");
 	r->nolighting = glGetUniformLocation(r->program, "nolighting");
+	r->grayscale_rate = glGetUniformLocation(r->program, "grayscale_rate");
 	r->alpha_mode = glGetUniformLocation(r->program, "alpha_mode");
 	r->alpha_texture = glGetUniformLocation(r->program, "alpha_texture");
 	r->uv_scroll = glGetUniformLocation(r->program, "uv_scroll");
@@ -1012,6 +1013,8 @@ static void render_particle_effect(struct RE_instance *inst, struct RE_renderer
 
 static void render_instance(struct RE_instance *inst, struct RE_renderer *r, mat4 view_mat, enum draw_phase phase)
 {
+	glUniform1f(r->grayscale_rate, inst->grayscale_rate);
+
 	switch (inst->type) {
 	case RE_ITYPE_STATIC:
 		render_static_model(inst, r, phase);
diff --git a/src/hll/ReignEngine.c b/src/hll/ReignEngine.c
index 79ec8c4..c0cd1db 100644
--- a/src/hll/ReignEngine.c
+++ b/src/hll/ReignEngine.c
@@ -2422,8 +2422,23 @@ static bool SealEngine_GetInstanceAlpha(int plugin, int instance, float *alpha)
 	return true;
 }
 
-//bool SealEngine_SetInstanceGrayscaleRate(int PluginNumber, int InstanceNumber, float GrayscaleRate);
-//bool SealEngine_GetInstanceGrayscaleRate(int PluginNumber, int InstanceNumber, float *GrayscaleRate);
+static bool SealEngine_SetInstanceGrayscaleRate(int plugin, int instance, float rate)
+{
+	struct RE_instance *ri = get_instance(plugin, instance);
+	if (!ri)
+		return false;
+	ri->grayscale_rate = rate;
+	return true;
+}
+
+static bool SealEngine_GetInstanceGrayscaleRate(int plugin, int instance, float *rate)
+{
+	struct RE_instance *ri = get_instance(plugin, instance);
+	if (!ri)
+		return false;
+	*rate = ri->grayscale_rate;
+	return true;
+}
 
 static bool SealEngine_IsExistInstanceMotion(int plugin, int instance, struct string *motion_name)
 {
@@ -2644,8 +2659,8 @@ HLL_QUIET_UNIMPLEMENTED(false, bool, SealEngine, IsThreadLoadingMode, int Plugin
 	    HLL_TODO_EXPORT(GetInstanceDiffuse, SealEngine_GetInstanceDiffuse), \
 	    HLL_TODO_EXPORT(GetInstanceAmbient, SealEngine_GetInstanceAmbient), \
 	    HLL_EXPORT(GetInstanceAlpha, SealEngine_GetInstanceAlpha), \
-	    HLL_TODO_EXPORT(SetInstanceGrayscaleRate, SealEngine_SetInstanceGrayscaleRate), \
-	    HLL_TODO_EXPORT(GetInstanceGrayscaleRate, SealEngine_GetInstanceGrayscaleRate), \
+	    HLL_EXPORT(SetInstanceGrayscaleRate, SealEngine_SetInstanceGrayscaleRate), \
+	    HLL_EXPORT(GetInstanceGrayscaleRate, SealEngine_GetInstanceGrayscaleRate), \
 	    HLL_EXPORT(IsExistInstanceMotion, SealEngine_IsExistInstanceMotion), \
 	    HLL_TODO_EXPORT(GetInstanceNumofBone, SealEngine_GetInstanceNumofBone), \
 	    HLL_TODO_EXPORT(GetInstanceBoneName, SealEngine_GetInstanceBoneName), \