When I was a student, my father decided to remarry. My new mother had a daughter younger than me named Nene. Nene treated me very naturally, even though I have a gloomy personality and don't say much. I was gradually Kokoro by her innocent, cheerful, kind nature, cute, and feminine curvaceous body. Then, one day, my parents decided to go on a slightly delayed honeymoon, and I ended up spending a few days alone with my step-sister Nene. I never expected it to turn out like that...