Blue Exorcist, Vol. 5 by Kazue Kato

Rin and his exorcist classmates are caught in a secret war against the forces of darkness.

Raised by Father Fujimoto, a famous exorcist, Rin Okumura never knew his real father. One day a fateful argument with Father Fujimoto forces Rin to face a terrible truth—the blood of the demon lord Satan runs in Rin’s veins! Rin swears to defeat Satan, but doing that means entering the mysterious True Cross Academy and becoming an exorcist himself.

In the late Edo Period, a demon known as the Impure King killed thousands of people. After defeating the demon, the Knights of the True Cross kept its left eye safely sealed away on Academy grounds—but now someone has stolen it! Hearing the thief has taken a child hostage, Yukio and Rin go to help. The investigation and pursuit will lead Rin and his friends to Kyoto and involve them even deeper in a sinister plot! But will his friends’ knowledge that Rin is the son of Satan drive a wedge between them?