Blue Exorcist 19

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.

Mephisto Pheles has freed his brother Amaimon from imprisonment and set him loose on True Cross Academy to serve his own agenda. While the Exwires deal with Amaimon's surprise reappearance, Lewin Light, a.k.a. "Lightning," continues to investigate the mysterious Section 13 and its connection to the Blue Night event that seems to be the source of all the current troubles. Together they delve deep beneath True Cross Academy, shedding light on long-lost chambers shrouded in darkness and the terrible secrets buried there for a reason...

The breakout manga and animation hit of 2011.