Transfer student Manabizaki Kyou is a swot, a person who spends too much time studying. His dream is to attend Tokyo University and then work for NASA! He will soon discover, however, that the high school he's transferred into, which was once very prestigious, has taken in delinquents from the surrounding schools. Now it is full of violence and gang fights.
Luckily, Manabizaki has a surprising skill at fighting, particularly when he's defending the peace of his study area. Through this strength he'll find his new friends, a weak boy called Iwashida and a legendary delinquent girl, Hasuno Nene, who makes him feel things that, for the first time in his life, he can't explain... (Source: MangaHelpers)

A boy who lost his memory is the champion user of the Otogi sport.

A samurai manga about a boy named Zan. Zan's father was a legendary swordsman who used a sword which had no edge (think Sakabatou from Ruroken). Zan's father died one day, and ever since, Zan has wanted to follow in his fathers footsteps.

The manga starts off with Zan being transfered to a new high school in his second year. When pushed, Zan somehow becomes super strong and has incredible sword technique that allows him to beat his enemies.