anime style, ultra-detailed, high quality, masterpiece, 8K, a young man, short black hair, black eyes, wearing a simple retro-style white shirt and short trousers, kneeling on wooden flooring in a traditional Showa-era Japanese room, playing with glass marbles, sunlight streaming through frosted glass windows, warm and nostalgic lighting, sliding shoji doors, vintage fan, low wooden table in the background, peaceful and innocent atmosphere, 昭和レトロ, still moment, focused gaze on the marbles, soft textures and warm color tones