The Book of Heroes(2010)

Miyuki Miyabe

A young girl travels into a magical world to save her brother from real-world bullies.

When her brother Hiroki disappears after a violent altercation with school bullies, the young Yuriko finds a magical book in his room. The book leads her to another world where she learns that Hiroki has been possessed by a spirit from the Book of Heroes. She visits the magical Nameless Land, where she is told how to save her brother, and is sent back to Earth with a young monk named Sora and the magical book, now a mouse named Azu. Yuri has to piece together the mystery of Horiko, and has a library of powerful magic books at her disposal to do so!