Age: 13 

Birthday: 4 July 

Blood type: A 

Ability: change trash into trees 

Kousuke Ueki is the main character in the series. He is in Class 1-C at Hinokuni Junior High School. Ueki's ability is given to him by Kobayashi (a.k.a. Mr. K), who is also Ueki's homeroom teacher.

Ueki is a genuinely kind person who is always trying to help people out. He is an unusually calm individual, and doesn't care about what happens to him. He can be found snoozing in class, letting children use him as a target for shooting soccer balls (or in one case, a surfboard) and also calling the police without panicking when he faces a gang of rowdy teenagers. He cares for people around him, even going as far as saving Robert Haydn from falling debris in the Dogura Mansion. He is a bit of a simpleton who constantly uses his ability against non-gifted, but that is because he just can't stand seeing these nasty folks 

defying his sense of justice. Even though he constantly loses his talents (and gains fairly useless ones when he wins), he believes that he can still make do by putting even more effort into succeeding. 

According to a short profile of the main characters of The Law of Ueki (published in the end of manga vol. 16 by the author), Ueki's hobbies include cleaning up his town. In the first volume of the manga, Ueki is seen planting trees in the town park.

Despite his power to change trash into trees may look weak in the eyes of others, it is actually quite different from other powers. Other power-users only have the ability to change item A to item B; for example from beads to bombs and from water to fire. But Ueki's power is different in the sense when he changes trash into trees, part of the tree can become trash, which he can change into trees again. In other words, it is a repeatable cycle.