History's Strongest Disciple Kenichi (Shijō Saikyō no Deshi Kenichi)
I'm surprised there wasn't any thread about this series in the Shonen section so I decided to do one !
Author : Syun Matsuena
Storyline [taken from wikipedia] :
The story focuses on Ken'ichi Shirahama (Shirahama Kenichi), an average 15-year-old weakling, whose life is upended with the appearance of the naive, beautiful, and strong transfer student, Miu Fūrinji. After Ken'ichi witnesses Miu's skills in martial arts, he joins the Ryōzanpaku dojo, a gathering place of those who are truly strong, which coincidentally also happens to be Miu's home. After beating a karate student in a match, he is soon targeted by all the delinquents in the school. Since then, Ken'ichi's daily routine is divided between his hellish training with the six masters of Ryōzanpaku, and his fights against the members of Ragnarok, a gang who views him as either a possible ally or an impending threat to their plans.
The story is really good, the fights are awesome and it's really funny ! The anime is fun to watch and the manga is finally starting to get scanlated at a pretty fast rate which is really nice.