When I was a student, my father decided to remarry. My new mother had a daughter younger than me named Miu. Miu treated me very naturally, as I was a dull guy with few friends and few words. I was gradually Kokoro by her pure, cheerful personality, 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 Miu. I never expected it to turn out like that...