Reborn!(2004)

Here Comes Reborn!

When Reborn, a fedora-wearing, gun-toting toddler, arrives and says he's come to groom Tsuna for his future as boss of an Italian organized crime family, Tsuna is more than a little skeptical. But Reborn may have the "magic bullet" necessary to turn Tsuna's life around!.

(Source: MANGA MILLION)

Note: Includes two extra collections of short chapters published in volume 42