From Viz:
A group powerful beings called tenkaijin are holding a special tournament. The rules of the game–each tenkaijin selects a kid in junior high to be his champion and grants him a special power. The kids take each other on in heated battle, but if they hurt innocent bystanders, then they lose one of their natural-given abilities. Every time they win a battle, they gain a new ability. The ultimate winner of the tournament is granted any power of his choosing, and the tenkajin who he represents succeeds in becoming the next god. Kosuke Ueki has been chosen to fight in the tournament. His special power–the ability to turn garbage into trees.