One of the Seven Angels of Punishment whose name means "Rigid One of God". He punishes sinners in Hell and uses a whip made of fire to punish nations. Kushiel along with the other angels of punishment are said to dwell in the third heaven according to the second book of Enoch.
Kushiel is the final boss of the Climax Theater quest, Persona Thief. He is Tamaizu Nirasawa's Persona, who has gone rogue due to Nirasawa's active imagination and believes himself to be the real archangel rather than a Persona. Kushiel's plan is to purge the Earth of humans who have forsaken God. In order to do that, he uses the power of rumors to make Nirasawa's belief that "covert government organizations have launched satellites to irradiate the earth with 'quantum plasma beams'" into reality.
Kushiel instructs Nirasawa to spread a rumor that "in Karukozaka High School, there is a handheld computer that can summon demons". By using the summoned demons to steal Personas, the minds of the students are emptied, thus allowing Kushiel to use the collective unconcious of the school as a super computer to calculate the targetories of the beams. Kushiel tells Nirasawa that the super computer will instead be used to calculate the love compatibility between him and the girl he likes. Nirasawa in turn entrusts this task to Haruo Weyland, who analyzes the stolen Personas in order to write new songs.
During the climax of the quest, Kushiel's plans are thwarted at the last second by Weyland, who sings an anthem to the students to decide what their own truth is, destroying Nirasawa's rumor. Afterwards, the party quells Kushiel by defeating him in combat.