The Demonic Beast (妖魔獣, Yōmajū) is the primary antagonist, an interdimensional entity aligned with the evil organization Uraer. Its exact nature—whether alien, demonic, or otherwise—remains undefined. The entity manipulates human behavior, exploiting societal issues such as bullying and gang violence within a private school system to corrupt individuals and incite teen suicides. Its motive is harvesting the victims' life force to sustain its own youth and power.

It manifests in a monstrous form. The Demonic Beast possesses the ability to traverse dimensions, frequently drawing human adversaries into a surreal, non-Earthly realm described as a gigantic, ruined hellscape or chessboard-like battlefield. This dimension serves as its operational base and facilitates confrontations.

The entity directly controls human agents, including Shiro Amakusa as its earthly proxy. Through Amakusa, it influences the student gang Jakoku-kai to perpetuate violence and despair. Its manipulation extends to the abduction and endangerment of human allies of the protagonist, notably the teacher Azumi Hazuki. The Demonic Beast engages in physical combat within its alternate dimension, strategically wielding the environment. It operates solely as a malevolent force, displaying no distinct personality traits, dialogue, or emotional range.

The Demonic Beast is defeated within the OVA’s runtime. It experiences no resurrection, evolution, or recurring appearances in sequels, spin-offs, or expanded lore. After its neutralization, its influence ceases. Affected characters like Azumi Hazuki return unharmed.