Katekyo Hitman Reborn!

A perfectly good manga that is slowly being ruined by its kiddy anime counterpart and numerous fangirls on fanfiction.net and Quizilla who enjoy writing shitty self-insert fanfics and horrible yaoi. However, the Japanese fans of this animanga are much better, as they can actually draw pictures and publish some pretty damn good doujinshi as well. Even most of the Asian fans, who usually come from the Philippines/Korea/China draw good fanart. The North Americans and Europeans mostly write fanfiction. 90% of the time it's a self-insert, and 10% it's an actual fic with plot.

80% of this fandom is yaoi, since there are very few female characters in the series. Also, most of the primarily GOOD fanfiction is on Live Journal. Katekyo Hitman Reborn! serializes in Shonen Jump! weekly but translations come out late most of the time. The main character is Tsunayoshi 'Tsuna' Sawada, a boy who is bad at academics and sports. He meets an infant hitman Reborn who later becomes his tutor, as Tsuna is to be the tenth boss of the Vongola family.

This manga is also interesting because it uses numbers in response to the character's names. For example, Tsuna is 27 because tsu= 2 and na= 7. Something like that. All in all, Katekyo Hitman Reborn! is decent for a manga. Although the fanbase is mostly made up of avid fangirls, the characters are memorable (and hot, even) and the antagonists are quite cool.

P.S. the Arcobaleno arc is a filler, SO STOP FUCKING ASKING IF THE MANGA AND ANIME WILL GO DIFFERENT WAYS NOW.