Plot
Tsunayoshi "Tsuna" Sawada, an unskilled and timid boy, is identified as the heir to the Vongola Family due to his direct descent from the organization's founder. The current Vongola boss, Timoteo, dispatches the infant hitman Reborn to Japan to tutor Tsuna and prepare him for leadership. Reborn employs a unique training tool, the "Dying Will Bullet" (死ぬ気弾), which forces its target to pursue their final regret with a powerful, resurrected determination. Through this method, the reluctant Tsuna gradually develops greater confidence and strength, making him a more suitable candidate. He forms close bonds with several schoolmates, including Kyoko Sasagawa.
His progression is challenged by various threats, beginning with a group of escaped mafia convicts. A more significant conflict arises with the Varia, the family's assassination squad, who support their own leader, Xanxus, for the position of Vongola boss. To confront them, Reborn enlists Tsuna’s peers to serve as his guardians: Hayato Gokudera, a dedicated bomber expert; Takeshi Yamamoto, a talented athlete who views their conflicts as a game; Ryohei Sasagawa, the boxing club captain; and the head prefect, Kyoya Hibari. They are later joined by the infant hitman Lambo and a mysterious girl named Chrome Dokuro, who is connected to the criminal Mukuro Rokudo.
Following this victory, Tsuna and his guardians are transported into a future where the Vongola Family is being systematically eradicated by the Millefiore family. They discover this was orchestrated by an ally of Tsuna’s future self to enable them to confront Millefiore's leader, Byakuran. Byakuran, who possesses knowledge from parallel worlds, seeks to collect all seven Vongola Rings to achieve omniscience. After defeating him, the group returns to their own time.
Tsuna is then formally recognized as Vongola X, but his inauguration is interrupted by the Simon Family, who seek vengeance for a perceived betrayal by the Vongola’s founder. This conflict is revealed to be a manipulation by Demon Spade, the first Vongola Mist Guardian, who sought to control Mukuro Rokudo and reshape the family. Tsuna and the Simon leader, Enma Kozato, unite to defeat him, mending the rift between their families.
Subsequently, Reborn and the other Arcobaleno become involved in a competition to lift the curse that binds them to their infant forms. The Vindice, enforcers of mafia law and former Arcobaleno, reveal the event is a selection process for their replacements. Tsuna and his allies defeat the Vindice’s leader, Bermuda. The entity known as Checker Face, who inflicted the curse, is revealed to be Kawahira, the administrator of a great power known as Tri-ni-set. He finds a new method to safeguard it and agrees to release the Arcobaleno from their curse.
In the aftermath, Tsuna declines the formal title of Vongola Decimo, and Reborn departs. However, Tsuna soon realizes that, while he remains unwilling to lead a mafia family, his experiences and the bonds he formed have fundamentally changed him. Reborn returns not to train a mafia boss, but to help Tsuna become a new kind of leader, the Neo Vongola Primo, with his trusted friends and partner at his side.
