Following his father's unusual directive, Shougo is enrolled in a school brimming with girls, tasked with finding a suitable partner. Mystery shrouds his birthday when an anonymous sender gifts him a cake, followed by a call from an unknown girl declaring sisterly affection. As it turns out, his long-lost sister is among his classmates, covertly vying for his attention. Will Shougo navigate this delicate web of relationships to reconnect with his sister and fulfill his father's wishes for romance?