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 his classmates succeed at the task gave to them by their teachers, but the camp is attacked by Amaimon, who holds Shiemi hostage to force Rin to fight. Having no option but to go full force against Amaimon, Rin is forced to reveal his secret by exposing his true form in front of his friends. With the other Exwires fleeing astonished after learning the truth about him, Rin easily overpowers Amaimon, but loses control of his flames and goes on a rampage. The Demon-Slaying Blade is cracked in the process.

Rin, Yukio, Shura and Arthur join forces to bring down the Gehenna Gate with no success. Meanwhile, demons keep coming through it and giving a hard time to the other Exorcists until the Esquires come with a plan to open a gate to Vatican, where is already daytime, and reflect the sunlight there to the Academy where is nightime to weaken the monsters protecting the Gehenna Gate. Rin and Yukio manage to seize these opportunity and when both unlock their demonic powers together, they fly through the gate and destroy it. One month later, things return to normal at the Academy and the Okumura twins return to the cave where they were given birth and pay a visit to their mother's grave.

After visiting their mother's grave, they meet an "evil spirit" in a highway. Rin appears from a highway cave with Kuro. The evil spirit then attacks Rin and Yukio. Rin destroys the evil spirit's first body and then the spirit takes control over a truck. Yukio shoots at the truck, Rin tell hims that there is somebody in the truck. Yukio says its just a dead corpse, but Rin believes the driver is still alive and that it's an Exorcist's job to protect people and defend against demons. He tells Yukio and Shura to find its weak point and charges after the monster.