The Vongola family is only one of many Mafia organizations in the Reborn! the universe and, as their position as strongest is always in contention, it's only right that their competition rises to the challenge.
With any great shonen comes great villains and rivals, and Reborn! is no exception. Like their boss, the development of these characters is at the series' forefront as well, with their fates always relevant to current events and just as interesting to observe when they are a chapter's focus. Hibari, Gokudera, Yamamoto, Ryohei and others possess unique personalities and powers that make their developments just as interesting to follow as Tsuna's. Tsuna makes a lot of friends this way, and similarly to the motley crews found in other Jump classics like Yu Yu Hakusho and Hunter X Hunter, the Vongola family is a lovable one. This zero-to-hero structure is used in Reborn!'s version of the Mafia underworld, and as such, Tsuna's evolution into one worthy of Vongola Decimo involves the recruitment of family members to serve as guardians.