Assiah, the realm of humans, and Gehenna, the realm of demons. Normally, these two dimensions would never intersect, but having possessed all material substances, the demons are now intruding on the material world. But among the human race, there are those who can exorcise such demons. - the Exorcists. Rin Okumura and his twin brother Yukio have been raised by Shiro Fujimoto, an eminent priest, so it comes as a shock when Rin discovers their biological father is actually Satan! As the border between "Assiah" (the human world) and "Gehenna" (the demon world) is crossed by evil, Rin vows to become the ultimate exorcist and defeat his own father. To hone his raw skills, Rin enters True Cross Academy to train with other exorcist candidates.
Blue Exorcist Vol. 1 (Bilingual Edition)
The ultimate weapon against Satan is his own son!