There are two worlds: Grimoires, where wizards live, and Grand Earth, where humans live. Theo, a boy who is human but suffers from a special constitution, visits the magical city of Grimoires to learn more about himself. There he meets the great wizard Lucas, who listens to him, but his constitution causes a terrible situation. He also discovers Lucas' surprising secret...! This is a story of the bond between a lonely wizard with a secret and a boy with a special constitution.