Marina, a high school girl who lived with her older brother, continues to live with him after he gets married and takes in a new wife named Akari. One day, Akari tells her that her brother has been cheating on her, which makes things awkward. Marina is also cheated on by her boyfriend. The two of them comfort each other and quickly become closer. Akari was originally bisexual, but she had stopped being bisexual after getting married.