NACT-075 English Sub: My gloomy older sister is curious about my penis!

My older sister, Natsuho, is always gloomy and shy. She has never made friends or worked a part-time job, and spends most of her time shut in her room. One day, I felt frustrated and annoyed with her, and I suddenly wondered what she was doing in her room, so I peeked through a crack in the door. There, I saw her using my naked body as a model. I was captivated by her incredibly sexy body, which I had thought was ordinary, and I just…