If you liked the Reborn! manga, the Anime-Planet community thinks you'd like:
Ever since Sena was little, everyone has treated him as an errand boy. His childhood friend, Mamori, even has to protect him from bullies all the time, although she's a girl. Fortunately, in order to evade his tormentors, Sena has developed incredibly fast legs; in fact, Sena is so fast that he is noticed by Himura, the quarterback of a failing football team, who promptly tricks him into joining. However, in order to keep other teams from scouting him, and to keep Mamori from finding out that he's in such a dangerous sport, Sena wears an eyeshield and goes by the name of "Eyeshield 21". For someone like Sena, making it in the tough world of football is a challenge like no other, but also the once-in-a-lifetime chance to become someone others respect!
If you liked one manga for its lead, you'll certainly like the other! A typical "zero to hero" scenario where the coward has to muster his courage and head out to battle and ultimately become a better man.
As a bonus, their "tutors" both happen to have spartan styles of training.
It's really difficult not to make parallels between Eyeshield 21 and Katekyo Hitman Reborn. For me, at least. The protagonists are quite similar: Dame Tsuna who doesn't display tremendous skill for anything, but has a big heart and Sena, and often bullied high school student also with a big heart. Both manga deal with the growth and maturation of the main character whilst making great friends on the way. Tsuna and Sena also look quite similar. Though the universes both deal with are vastly different and some themes vary, there's a very similar large underlying. Both series are fun to read and have memorable characters.
Shirihama Kenichi is a weak scaredy-cat, and his status as the karate club's punching bag has earned him the name of ‘Weak Legs'. One day Kenichi meets Miu and, impressed by her skill after she effortlessly throws him to the ground, he follows her to the Ryouzanpaku dojo. There he finds five great masters of martial arts, and driven by his desire to become stronger, he begs them to accept him as their student - though it won't be easy. Kenichi endures harsh training (and injury) from Akisame - the philosophizing Jujitsu master; Apachai - the Muay Thai ‘God of Death'; Kensei - the ecchi Chinese Kempo Master; and Shigure - the weapons prodigy. Finally after proving his determination, he is accepted by Shio - the 100-dan Karate Master, who had initially wanted nothing to do with him. Now Kenichi walks the long and arduous path to becoming a master himself, all whilst trying to protect those he cares about from anyone who would dare to harm them.
Kenichi and Reborn! both star incredibly timid and weak high school boys. Both Tsuna and Kenichi also are motivated by their feelings for their friends and especially the girl they like. The battles get more extreme as each series progresses and the comedic nature stays strong throughout the series.
Drawn to the mystique of the unknown, Hunters travel the world in search of terrifying creatures, incredible riches, and unexplored lands. Gon Freecss is a naive-yet-determined young boy who aspires to join the ranks of these individuals, in order to find his missing father Ging - a master of the profession himself. To reach his goal, he partakes in the formidable Hunter Exam, a series of tests that push the participants to their physical and mental limits, with a Hunter License as the prize. During the exam Gon befriends vengeful Kurapika, doctor-to-be Leorio, and skilled assassin Killua, who have entered for their own reasons. But with the sinister Hisoka standing in their way, will Gon and his friends be able to succeed in obtaining their reward, or even escaping with their lives?
Hunter x Hunter and Reborn! both have a unique style of fighting. They both begin with regular fist fights, but as the series progresses the fights get more extreme by using Ren or Dying Will respectively. Each character has his own unique weopon and grows stronger as the shows progress.
Both of those shounen battle mangas start with almost identical setting. The main hero is a weak, bullied and cowardly kid who suddenly learns, about his amazing lineage and mysterious power he can inherit ( mafia family Vongola in Hitman Reborn, strongest magical king in Hyde and Closer).
Due to this sudden development many assasisns targets young boys live. To keep him alive he receives a guardian in childish body (Teddybear Hyde in Hyde and closer and child Reborn in Hitman Reborn). This guardian, despite his appearance, is powerful being and skilled teacher, who will direct young boy towards his powers.
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.