Karukozaka High School disappeared into the Underworld six months ago, taking 560 students and 28 faculty members with it, and was never discussed again. However, two students - the perceptive demon-smelling boy, Nobu, and Yumi Shirakawa - returned unnoticed. In an effort to move on from the disturbing incident, they severed contact and transferred to different schools while still keeping an eye out for demonic activity.
Sadly, the reopening of the portal to the Underworld at their old school sows chaos that both the Ring of Gaea and the Order of Messiah seek to capitalize on. The former aims to secure Tokyo by imposing martial law to deter demons, but the latter perceives Nobu and Yumi as a threat to their plans for a new world. Nevertheless, after a demon kills his mother right before his eyes, Nobu realizes he cannot run from his past and must confront it.
