Nagi Umino and Erika Amano, teenagers swapped at birth and now engaged instead of returned to their birth families, settle back into their crowded shared household with Nagi’s sister Sachi and his crush Hiro Segawa. The fragile routine breaks almost immediately when Nagi’s childhood friend Ai Mochizuki returns from abroad and declares she intends to marry him. This season picks up directly after the first, with Nagi’s living situation now open to a fourth complication.