Ao no Exorcist: Yuki no Hate-hen

Demonic activity worldwide has significantly increased due to the involvement and corrupt practices of the Illuminati. To combat the unnatural influx of demons, the Vatican Headquarters decides to hold the annual Exorcist Certification Exam early and allow for as many exorcists as possible to take up the mantle.

Straight from the Vatican, one of the most powerful exorcists, Lewin "Lightning" Light, arrives at True Cross Academy to help prepare the students for the exam. The ease and mastery with which Lewin performs exorcisms quickly impresses Ryuuji "Bon" Suguro, who has lost his ambition to continue his studies, and Lewin surprisingly accepts him as his apprentice. Amid the worsening situation, twin brothers Rin and Yukio Okumura are sent to locate the recently missing exorcist Shura Kirigakure, who seems to be chained to a decades-long contract with a powerful, immortal demon hiding in Aomori Prefecture's dangerous, snowy mountains.