Rin Okumura is a teenager with a natural gift to get himself in trouble. Despite that he tries his best to meet the expectations of his twin brother Yukio and Priest Shiro Fujimoto, who acts as their guardian, until he finally learns about the dark secret behind his origin.

Fujimoto and his companions try their best to protect Rin from the demons who are after him, but he ends up posessed by Satan, the most powerful of the demons and Rin's father. Seeing his guardian taking his own life to protect him fron Satan, Rin decides to fight back by unlocking his demonic powers, even knowing that by doing it he would not be a human anymore.

Having Shiemi as a new classmate, Rin's total disregard for classes brings forth the anger of another classmate of his, Ryuji Suguro, aka "Bon". After learning of Bon's story, Rin finds that they have more in common than he would like to admit.

Rin and Yukio find that the responsible for their meals at the dormitory was Ukoback, a cooking familiar appointed by Mephisto Pheles to aid them. They also learn how Ukoback can be troublesome when he gets angry.

Shura Kirigakure, a high level Exorcist and former apprentice of Father Shiro was acting as one of Rin's classmates tasked to investigate his connection with Satan. With orders to kill him if it were proven true, she is divided between fulfill her obligations and follow Shiro's request to look after Rin in his place if something would happen with him. Her doubts are cleared when she confronts Rin and finds that Shiro was actually raising him like a son instead of a weapon.

As the hearing drags on, the Order finds itself unable to decide on Rin's fate, as Mephisto has proclaimed him to be "a weapon for counterattacking Satan." Just then, something happens…!

Rin undergoes training to master his demonic flames, when a giant bird-like demon swoops in on him! After driving it away, all of the Cram School members are sent to investigate how the demon infiltrated the academy...

The assailant has escaped, but things are just getting back to normal after the monastery attack. Just then, someone appears before Yukio!

In light of the recent incidents, Mephisto is dismissed from his post as director. The Order’s Supreme Advisors are ousted as well, paving the way for Ernst to become Pope. And the newly appointed Preceptor of the Japan Branch is revealed to be...

Ernst is scheming to open the Gehenna Gate by using the blood of Rin, son of Satan. In order to protect his wounded older brother, Yukio offers to take his place.

Hordes of demons are spilling out of Gehenna Gate, and are now indiscriminately attacking the people of True Cross Academy Town! Meanwhile, Rin has been rescued by Suguro and Shiemi and is starting to come to. What Rin sees when he awakens is...

Satan has transformed himself into a gigantic Gehenna Gate, and is attempting to absorb all of Assiah. Rin and Yukio, joined by Shura and Angel, attack the gate. Meanwhile, at the school, the exorcists defend against a myriad of demons.