Etou, a fat and unattractive student, has feelings for Sayako, his popular and friendly classmate. While wandering at night, he sees Sayako being harassed by some men. Initially reluctant to get involved, he ends up helping his classmate. However, when they are safe, Etou realizes that Sayako is very different from the one at school. The truth is, she has a dual personality; during the day, she's a modest and kind student, but during the night she is a vulgar girl with a lot of sexual desire. Now that they are both alone, Sayako shows her lust and fucks Etou.