Reborn (リボーンRibōn?) is an Arcobaleno and the holder of the Yellow pacifier of the Sun. The titular character, Reborn is an infant hitman belonging to the Vongola Family. As the Vongola IX's most trusted member, he becomes Tsuna's home tutor and trains him into becoming a Mafia boss. He often shoots Tsuna with special bullets that enhances his abilities . Since Reborn is not an official Vongola member and is only there to train Tsuna, he is not allowed to directly interfere with most of Tsuna's battles, though he is allowed to defend against attacks directed solely at him. His "partner" is a shape-shifting chameleon named Leon (レオンReon?), who usually sits on Reborn's fedora. The bullets used by Reborn are created inside Leon. When Reborn's student is gradually progressing, Leon's tail falls off, his shape-shifting abilities become unstable, and he is no longer able to create bullets. After Leon creates special items for the student, he returns to normal. In the future, Reborn is mentioned to be dead, and in order to avoid the Negative Seven Rays which Byakuran unleashed in the atmosphere in order to slowly kill the Arcobaleno, the past's Reborn remains in Vongola's underground base and wears a special suit.

No matter how strong the emotion, Reborn always keeps a straight face and handles many situations as calmly as possible. Reborn often says "Ciaossu" (a mix of the Italian "ciao" and the Japanese "ossu", which is a casual male greeting). He randomly appears dressed as "another person" who no one except Tsuna and Dino recognizes, and seems to see nothing unusual in any of his own behavior. He is normally voiced by Neeko in the anime but in his short appearances as an adult, Ken Narita voices him.