Fifteen-year-old Kishimoto Kasumi had planned to reside with her aunt from April onward to attend high school. However, upon arrival, she discovered that four new male students had already taken up residence in the household. Worse still, while bathing that day, one of the boys, Takasugi Yusaku, walked in on her, exposing her nakedness and setting the tone for Kasumi's difficult high school experience.