In the winter of his fourth year of college, his classmates reunite for the first time in five years at a class reunion. The protagonist, Takao, has not yet received a job offer and attends the reunion with mixed feelings. Mayu, his girlfriend at the time, is also there. There, Takao learns a shocking truth. To his surprise, Mayu has been having sex with almost all the boys in her class. Another side of her that I don't know.