Katekyo Hitman Reborn!
What I loved most about the manga was that it never forgot its origins and it stayed true to the characters established. Tsuna is ever the reluctant hero, constantly doubting his value and the position he holds with his friends, his 'family'.
Though he does develop, coming into his own as a powerful successor to the Vongola mafia family, he constantly laments the fact that he must participate at all. It is only upon Reborn's insistence and for the safety of his friends that Tsuna ever really acts. By the end of the manga, Tsuna is still adamantly refusing to step up as the new head of the family.
Ultimately, I do hope for more Reborn! i nthe future, though that seems unlikely.