Zatch Bell! - Makoto Raiku

For his 14th birthday, Kiyomaro received a bizarre present from his father - a strange little boy named Zatch Bell. Zatch's mission is to reform Kiyo's bad attitude and help him make friends, but Kiyo soon discovers that there's more to Zatch than his dad ever realized. Zatch is a creature called a mamodo, and he has magic powers that are unleashed when Kiyo reads from a mysterious red book. With Kiyo's help, Zatch must compete against the 99 other imps like him who are vying to become the king of the mamodo world! As the battles with the other mamodo intensify, Kiyo's loyalty to Zatch is put to the test. And what will happen when the red book is stolen?