B Gata H Kei revolves around lascivious 15-year-old high school student Yamada, who makes it a goal to have sexual relations with 100 different guys. However, her insecurities as a virgin herself lead her to reject every guy who attempts to make a move on her. To overcome this mental barrier, she searches for a "cherry boy," an inexperienced guy who will be her first. At the bookstore, she falls on her rather plain classmate Takashi Kosuda, and makes him the target of her seductions.