Rent Kenichi: The Mightiest Disciple: Series 1 (2006)

Can this weak-kneed boy become the greatest martial artist of all time? Yeah, Kenichi's a total wimp. He's always getting picked on and doesn't have a lot of friends to stick up for him. The guy needs motivation if he hopes to graduate in one piece. Well, Miu's the perfect motivation. She's hot, she accepts him, and she just so happens to live at a dojo with six martial arts masters. You could say fate has led Kenichi to their door, or you could say he was just following the hottie. Either way, he's about to get whipped into serious shape. If he can survive some hard-core training, he might survive another day at school. He might even score with Miu. Yeah, you could call Kenichi a wimp. But let's go with underdog instead.