Daiki, who works part-time as a bartender at joshidaikoji (meaning Women's college alley), discovers a junior high school student in cardiopulmonary arrest in a park while wearing a cosplay costume. Since it was three days after the dead body of a junior high school student was found at the same place, Daiki is brought in by the police as a suspect in a serial murder case. His sister Mio, who works at a club in Yanagase, saves him from this predicament. The two sisters always quarrel whenever they meet, but in order to prove their brother's innocence, they pursue the real culprit in the case.