Ryu Kutou is the composed and charismatic president of the student council at Hell's River Styx Academy in Destinyland. He initially appears sympathetic to protagonist Linne Amagane after her arrival. Human and capable of bleeding, he has gathered fellow humans within the council.

His true identity is Abel, the biblical son of Adam and Eve. He harbors an ancient grudge against humanity stemming from his murder by his brother Cain, revealed as the headmaster Helvis. Helvis once imprisoned Abel's madness and immense power within a giant pulsating mass.

Ryu orchestrated Linne's arrival in Hell, knowing she is the reincarnation of his mother, Eve. His ultimate plan is to end the cycle of reincarnation using Stealer, a being he created wielding the power of Nothingness. He activates Stealer to absorb all souls in Hell for permanent erasure, transforming the realm into a funnel-shaped pit drawing inhabitants towards annihilation.

He reveals Hell exists solely due to his influence. Through religion, art, and philosophy, he cultivated humanity's belief in Hell as a place of punishment, ensuring souls would self-inflict damnation. This construct served as both his prison and the manifestation of his enduring resentment.

His plan is ultimately thwarted. Stealer, influenced by Linne's kindness, rejects her role as an instrument of destruction and sacrifices herself to stop Ryu. This sacrifice consolidates and destroys the negative energy Ryu channeled, restoring Hell and allowing Linne to graduate and return to the living world. Ryu's defeat ends his attempt to obliterate souls and disrupt reincarnation.