One day at school, Kasumi was threatened by a man, demanding that she pay him back the debt that was left by her father or that she pay in kind. Okura saw his beloved teacher being threatened and helped Kasumi chase the man away. Okura plans to help her and gives Kasumi the money to repay her debt. However, she declines his offer, not wanting to involve anyone else. Okura, afraid that the girl he is in love with will get away with it, decides to buy her himself. Paying her money to have sex with him. Now Kasumi is his faithful sex slave. What's missing though is something else, namely her younger sister and Okura's classmate the cute girl Kaho.