The story revolves around a boy named Tsunayoshi "Tsuna" Sawada, who is chosen to become the Vongola (Italian clan) Family's boss due to him being the great-great-great-great grandson of the first Vongola boss, who had moved to Japan from Italy during his own time. He is told by Reborn that he will become the tenth (Italian decimo) Vongola boss. Also, the other candidates for the position of the head of the Vongola Family have died. For these reasons, Tsuna is the only remaining heir. As such, Timoteo a.k.a. "Vongola IX", the current head of the family, sends Reborn, an infant hitman from Italy, to train Tsuna.