In Cosmic Era Year 6,660,000, the God of Evil—an infamously sinister mastermind—was just one step away from killing the God. However, one day, he suddenly lost most of the magical powers and was transformed into a baby. To regain the lost power, activates the own custom-built resurrection program, an alternate-dimension ritual known as Demons' Night Fever, and decides to use Killshiro as a disciple.

A corporate slave programmer in a third-rate exploitative game company, who harbors a deep hatred for the world. He mistakes the entire ordeal for a bizarre, stress-induced hallucination, and decides to embrace his role as the Devil's disciple to vent his frustrations on the real world. Furthermore, due to the adjustments of the ritual takes place—reveals his true mental age: stuck in middle school, which manifests as his appearance in this world.

A world-famous, popular idol overflowing with a strong sense of justice, who shares a past with Killshiro as a former middle school classmate. God has convinced her that "Killshiro is brainwashed by the Devil," and she blindly believes that her holy mission is to save him from the Devil’s grasp. Wielding the new powers granted by God, she steps into battle to strike down Killshiro and his allies, who she believes have been unwillingly enslaved by the evil Devil.

An entity that has been in a long-standing conflict with Giga Super Death.
He gathers deep faith from the people by posing as a saint , but repeatedly commits various acts of sabotage in an attempt to erase Giga Super Death on behind. To completely obliterate the baby Giga Super Death from existence, he manipulates his disciple, Mary, with clever words, frequently standing in Killshiro's way.