Blue Exorcist Humans and demons mirror each other just as their worlds, Assiah and Gehenna, do. Travel between them is only possible through possession, but Satan lacks a suitable host and remains trapped—so he sends his son to Assiah, hoping he’ll grow into one. The story follows Rin Okumura, a seemingly normal troublemaker who learns he’s Satan’s son after being attacked by demons. Rejecting his father’s plan to conquer Assiah, Rin instead begins training as an exorcist, determined to protect his world alongside his brother Yukio.