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, without realizing that she might actually develop true feelings of love for him.