Mullin, a young demon serving as Beelzebub’s devoted head attendant in Pandemonium, sports pale skin, vibrant lavender-purple hair, and small, piercing emerald eyes. His uniform features a blue frilled blazer, matching pants, dark boots with pink soles, and a white scarf later gifted to Beelzebub in a tender act of care. A stickler for efficiency, he relentlessly imposes order on Beelzebub’s chaos, clashing with her whimsical antics—from her penchant for fluffy creatures to her habit of discarding decorum, most notably sleeping unclothed. Beneath his exasperation lies unwavering loyalty and simmering romantic longing, frequently leaving him flustered by suggestive situations. His tsundere nature and “maiden’s pure heart” make him a target of teasing, especially regarding romance or exposure.

Hailing from Pandemonium’s civilian sector, Mullin was raised by an unnamed mother alongside twin sisters and their family’s fluffy dog. He guards his siblings with protective fervor, a trait that caught Beelzebub’s admiration. Though his early years remain shrouded, his steadfast discipline implies a rigorous upbringing.

Charged with safeguarding his liege, Mullin once intercepted thugs harassing her, an act that ignited her romantic interest. Their unspoken mutual attraction persists in delicate tension. His arc transitions from rigid formality to measured tolerance of Beelzebub’s eccentricities, epitomized by the scarf’s symbolic transfer marking emotional vulnerability.

He demonstrates social flexibility, having initially mistook Azazel for conventional masculinity before recognizing his affinity for adorable trinkets. With figures like Belphegor and Eurynome, he maintains calibrated professionalism, negotiating obligations against personal limits. No expanded portrayals in ancillary media exist.