Reborn!, known in Japan as Katekyō Hitman Reborn! is Japanese manga written and illustrated by Akira Amano. Reborn! has become one of the best-selling Weekly Shōnen Jump manga with several of its volumes becoming top-sellers in Japan.
The Reborn! story revolves around a boy named Tsunayoshi "Tsuna" Sawada, who is chosen to become the Vongola 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 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.
The current Vongola boss (Timoteo a.k.a. "Vongola IX",) thus sends his most trusted member, the titular character and infant hitman, Reborn, to train the future boss. Tsuna then unwillingly undergoes training from Reborn. Reborn's main method of teaching Tsuna is the "Dying Will Bullet", which will make the person be "reborn" with a stronger self intent on fulfilling his dying will. Through his experiences, the initially clumsy and underachieving Tsuna unconsciously becomes stronger and more confident, which ultimately makes him better suited as the Vongola Family's boss despite continuing to reject his Mafia inheritance. Tsuna gradually becomes a more confident person and leader, while Reborn slowly recruits members into Tsuna's own Mafia family, which mostly includes Tsuna's schoolmates. Tsuna goes through many predicaments in his progress of becoming the Vongola boss including fighting against escaped Mafia convicts posing as Kokuyo Junior High students. Though they encounter new allies in the form of other hitmen and mafiosi, they also attract attention from those who want to annihilate the future boss of the Vongola Family.
The Varia, Vongola assassin squad, claim the right for their boss, Xanxus to be the true Vongola boss, and start a competition to decide it. To defeat the Varia, Reborn recruits most of Tsuna's schoolmates to become the Vongola guardians: Hayato Gokudera, a dynamite expert who wishes to be his right-hand man, Takeshi Yamamoto, a baseball player who thinks the Mafia is a game, Ryohei Sasagawa, the energetic captain of the school boxing club, and Kyoya Hibari, the deadly head prefect. Lambo, a weak infant assassin who came to kill Reborn, and Chrome Dokuro, a girl who has a mental and physical link with the criminal Mukuro Rokudo, joins them as well.
When the story later shifts into an alternate future, nine years and ten months later, in which some of the characters are transported into, they have to adapt to a world where every Vongola member, as well as their allies, is being hunted down by a powerful rival family of that era, the Millefiore. They also find that all the Arcobaleno are dead except for Reborn from the past. As Tsuna and the Vongola Guardians from his time fight the Millefiore they learn that Shoichi Irie, a comrade of Tsuna's future self, was the one who sent them to the future as the future Tsuna said they were the only ones who can defeat the Millefiore leader Byakuran. It is later revealed that Byakuran has gained knowledge from parallel worlds and that he wants to obtain all the Mafia rings in order to obtain a power similar to omniscience.
After defeating Byakuran, Tsuna and company return to the present where they learn that Tsuna is to undergo the inheritance ceremony to officially become the 10th boss of the Vongola Family. However, the ceremony is attacked by the Shimon Family, who have sworn revenge on Vongola Primo for supposedly betraying the first Shimon boss. Using the power of the Shimon rings, they have destroyed the Vongola Rings, left Yamamoto hospitalised and kidnapped Chrome. However, a man named Talbot reconstructs the Vongola Rings into the Vongola Gear, and Tsuna and the remaining guardians go to Shimon's hideout where they must face the Shimon family in battles with their pride on the line. In addition, whoever loses in either side will be taken away by Vindice into prison forever. While the various battles take place it is revealed that Daemon Spade, a member of the first generation Vongola boss's family, is the one who kidnapped Chrome and has a dark agenda in the battle between these rival families.
Reviewers from the series praised its use of comedy as well as the designs used for the infants’ characters. Some attribute the story's humor to the peculiar characters with one reviewer positively describing it is as an insane collection of characters. They also mentioned that though it has become more violent since volume 8, it has turned into a better shōnen series, praising the storylines and the fights.