Sullivan, a high-ranking demon and principal of Babyls Demon School, holds dual authority as a member of the Thirteen Crowns and one of the Three Greats, revered as one of the demon world’s most formidable figures. Though his power and political influence position him as a prime candidate for Demon King, he deliberately remains at rank Tet (9), adhering to a cryptic directive from the vanished Demon King Derkila, who once dissuaded him from pursuing succession. A towering presence with a bald head, curved yellow horns, and a white handlebar mustache, Sullivan’s sharp pince-nez glasses veil his eyes. His dark purple fur-collared suit and bird-skull adornment exude authority, though his form shifts whimsically between a rounded, comical silhouette during jovial moments and a razor-edged, menacing figure when unleashing his might. Beneath his playful antics lies a shrewd strategist. Motivated by envy of peers Levi and Belial’s grandparenting tales, he adopts Iruma Suzuki, a human boy abandoned by his parents. What begins as a whimsical ploy deepens into genuine devotion; Sullivan lavishes Iruma with affection and protection, concealing his human identity through magic and thwarting threats like Six Fingers operative Atori. Central to his past is his bond with Derkila, whom he served as loyal advisor. Their relationship, mirroring his current dynamic with Iruma, anchors his refusal to claim the throne despite his qualifications. Subtle hints of unresolved history—a potential curse, lingering tensions—linger around Derkila’s disappearance, driving Sullivan’s quiet campaign to groom Iruma as a prophesied successor. His arsenal spans gravity manipulation, time stoppage, teleportation, and conjuring shadow entities for combat. Keen magical perception detects distant threats, while his aura alone can immobilize powerful foes. A master tactician, he dismantles terrorist networks through spies and sways the Thirteen Crowns with diplomatic finesse, advocating Iruma’s potential. In alternate narratives like the Mafia AU, Sullivan commands criminal empires with the same duality—dotingly paternal yet ruthlessly authoritative. Across all incarnations, he evolves from an eccentric administrator to a linchpin in the demon world’s political landscape, tempered by his disciplined assistant Opera, who curbs his impulsiveness. Threaded through his actions—whether mentoring Iruma in the Heartbreaker Competition or countering schemes by rivals like Baal—is a pursuit of legacy and redemption. Balancing calculated ruthlessness with unexpected mercy, Sullivan navigates power struggles to stabilize the demon realm, honoring Derkila’s memory while shaping its future through Iruma’s ascent.