The Law of Ueki

In a world of powerful celestial beings, an epic contest is being conducted to select the next king! Each Celestial selects a kid in junior high to be his champion and grants him a special power. The kids battle it out--losers are eliminated, and the winners are granted new talents! Seemingly ordinary Kosuke Ueki has been chosen to be a contender in the tournament. Granted the power to change trash into trees, Ueki has two disadvantages to overcome--one, he doesn't know he's a participant in the tournament, and two, how the heck can anyone win a battle with the power to turn trash into trees? (Source: VIZ Media)

Two years after the tournament of the next god, Kosuke Ueki is now a 3rd year student in Hinokuni High School. For some reason, everyone in the real world has lost their memory of their most important person, including his friends, who participated in the tournament two years ago. Ueki, being the only person left in the world unaffected, is fighting in order to restore everyone's memories. Ueki follows a little sheep named U-lu to another world called Hankagai. There, he meets new companions and gains new powers. (Source: Wikipedia)