Katekyo Hitman Reborn anime series follows the life of a young boy named Tsunayoshi "Tsuna" Sawada, who finds out that he is the next in line to become the boss of the most powerful Mafia organization, the Vongola Family.
Also, the other candidates for the position of the head of the Vongola Family died: Enrico, who was the leading candidate to become "Vongola X", died in a gun battle; Massimo, the second, "sleeps with the fishes;" and Federico, the favored son, was found as a pile of bones. For these reasons, Tsuna is the only remaining heir. As such, Timoteo a.k.a. "Vongola IX," the current head of the family, sends the Vongola's most powerful hitman--a gun-carrying infant named Reborn--to tutor "Tsuna" on how to become a respectable boss.
Tsuna then unwillingly undergoes training from Reborn. Tsuna goes through many predicaments in his progress of becoming the Vongola boss including fighting against escaped Mafia convicts, a rival group of Vongola assassins claiming the right for their boss to be the true Vongola boss,rival families aiming to destroy the Vongola Family, and a new family in the future that nearly decimates the Vongola. Through his experiences, Tsuna unconsciously becomes stronger and more confident, which ultimately makes him better suited as the Vongola Family's boss, although he continues to reject his mafia inheritance... or won't he? You'll have to watch Katekyo Hitman Reborn to find out =P...