It starts when the three of them bond as Gikyodai (associate with each other as brothers) under a plum tree in connection with the tradition of 'Oath of the Peach Garden' in the "Romance of the Three Kingdoms."
『三国志演義』の「桃園の誓い」の故事にちなみ、梅の下で義兄弟の契りを結んだところから話がはじまる。