Book Eater

Theodore Miller knows everything about magic... except how to use it. Just as he's about to flunk out of Berghen Academy, Theo chances upon a grimoire named "Gluttony" that manifests as a magic-hungry creature on his hand. The more magical texts and artifacts Gluttony consumes, the more powerful Theo becomes, quickly making him the academy's star student. Sure, he now lives under constant threat of being eaten by an insatiable parasite, but Theo is finally on his way to becoming a real wizard.