The story of Yui Tachibana, who agrees to be held by a perverted teacher to protect the dream of her boyfriend and childhood friend, Kou Takanashi. The day Kou loses a match, Yui is summoned by the perverted teacher to visit her room. She does it because of a promise they made to each other. Soon, the two fall into a lascivious session of unfaithful sex, with a mixture of humiliation, anguish and pleasure.