If you're looking for manga similar to Reborn!, you might like these titles. All recommendations are made by Anime-Planet users like you!
Rikuo grew up in a house full of yokai, so he always thought they were cool. But the kids in his class talk about yokai like they're bad! When his grandfather announces Rikuo as his chosen heir to run the Nura clan, Rikuo is torn between his human nature and his duties as a yokai. The rest of the clan's not so crazy about a wimpy part-human as their ruler, particularly Gagoze, a high-ranking yokai who would rather eat a human than be ruled by one.
Both Reborn! and Nuraihyon no Mago have a similar feel between them. They both are about young and weak boys becoming the next head of a top mafia family (Reborn of the human world, and Nuaihyon of the demon world). They both have personality changes, respected older "brothers" to guide them, and a lot of action. But putting all of that aside, they just remind me of each other, between the plots and rivals, and all the lives at stake. If you like one, you should give the other a try.
Once, the ninja village of Konohagakure was attacked by an evil nine-tailed fox spirit. This demon slaughtered many people until the leader of Konohagakure, the 4th Hokage, sacrificed his life to seal the fox inside a newborn child - Naruto Uzumaki. Now, twelve years later, Naruto is a member of the Ninja Academy; but due to his past Naruto is shunned by the rest of the village, and since he has no friends or family he plays the part of class idiot to get attention. However, he is determined to gain respect by becoming the next Hokage - the most powerful shinobi in the village. With his apparent lack of abilities, will Naruto be able to realize his goal through determination alone?
Both of the main characters start out as the weakest of all the characters and end up as the most powerful characters of their series. All the battles in both series create growth within all the characters. And they both have a good balance of humor and action.