Katekyo Hitman Reborn!, Shijou Saikyou no Deshi Kenichi Recommendations
its similar in the way that is about a boy(good for nothing coward boy) and has no friends and gets pick on a lot in school then he gets a master(s)(tutor) and by training that boy starts the road to become the greatest strongest (fighter)mafia boss in the world and gets to meet friends along the way and this friends being strong fight by his side
Both of these manga should be more popular than they are. Both of these have very similar themes, and quite frankly if you're a fan of one piece or naruto I think both of these would be good to read as well. However I am recommending katekyo Hitman Reborn if you like History's Strongest Disciple Kenichi because they are so similar to eachother.
Both have a really weak main character that is super whimpy in more than one way at the beginning. Both main characters have no friends but earn them as the story progresses. Both main characters get stronger for the sake of protecting the