Blue Exorcist, Volume 10 (Blue Exorcist #38-41)

With the defeat of the Impure King, the Exwires have returned to their routine lives back at True Cross Academy - but the routine doesn't last for long! Halfway around the world, a strange encounter in the desert is the harbinger of evil things to come. An upturn in supernatural incidents at the academy involves Rin and his friends, but their seemingly simple tasks are about to draw them into a far larger conspiracy. Powerful forces have begun to awaken and an old enemy prepares for a new conflict.