Kasai

The most violent and perhaps the strongest of the 4 Heavenly Kings, Kasai is filled with an all-consuming need to prove himself and keep the respect of his classmates by beating up anybody that he considers strong. The school he goes to has the worst reputation in all of Tokyo and is considered a Yakuza recruitment ground. Having dominated everybody in Ikebukuro he decides to once and for all prove who is the strongest of the 4 Heavenly Kings by humiliating each and every one of them. His rage and his desire to be number one starts to overwhelm him and destroy his sanity and his friendships.

(Source: Wikipedia)