Katekyo Hitman Reborn!, Juhou Kaikin!! Hyde & Closer Recommendations
The two mangas are based around two cowards who are forced to become stronger to become the boss or master of a supernatural group. The only differences is that Hyde and Closer focuses on magic while Reborn! focuses on the mafia.
Both have little guys that are over power (Reborn and Hyde), two losers (Tsuna and Closer), and the losers are importants. Both are comedy manga (KHR, in the start).