B Gata H Kei revolves around 15 year old high school student Yamada whose lascivious nature causes her to aspire to one day achieve sexual relations with 100 different partners. However, her insecurities as a virgin leads her to reject every guy that attempts to make a move on her.
In order to hurdle this mental barrier Yamada goes on a search for her "golden cherry", an inexperienced boy whom she will bestow the right to be her first. One day while perusing a bookstore for the replacement of a dictionary she had defiled by highlighting all the sexual terms, Yamada has a fateful encounter with classmate Kosuda Takashi. Believing that Kosuda is the boy she is looking for Yamada goes to great lengths to try and seduce him. All the while, she discovers the difficulties in making that first important step towards reaching her goals, not to mention, finding out her true feelings for Kosuda Takashi.