Blue Exorcist - Shimane Illuminati Saga -

Rin and his friends successfully defeated the Impure King after his revival in Kyoto and have returned to their daily lives at True Cross Academy. However, the Knights of the True Cross begin receiving an increasing number of consultations about demons as a wave of strange events begins to spread across the world. Meanwhile, Rin and the other Exwires work to solve the mysterious phenomenon plaguing the school. But as the True Cross Academy Festival is in full swing, Lucifer, the King of Light and Commander-in-Chief of the Illuminati, suddenly appears. Lucifer declares war on the Knights of the True Cross – to resurrect the demon god Satan and rejoin the realm of humans, Assiah, and the realm of demons, Gehenna, as one. And to do so, he states that Izumo is necessary for a certain “plan". (Source: Aniplex)