Subaru takes it upon herself to enroll in an all-boys high school to fill in for her brother who is currently under hospital care. As she starts her first day, she is introduced to a group of peculiar individuals. The moment they find out her name, they seem surprised and demand that she be a part of their Lion Club. Concealing her gender was already difficult enough, but now she has to deal with this eccentric group who claim to have been part of the Shinsengumi in a past life.