Opera functions as the security demon for Sullivan, one of the Three Greats governing the Netherworld during the Demon King's absence. Residing in Sullivan's mansion, they manage household duties including laundry, cooking, scheduling, and transportation for Sullivan and his adopted grandson, Iruma Suzuki. Their core duty involves protecting Sullivan's life, status, appearance, and reputation, later extending this protection to Iruma after the Akudol Games. While Opera's official rank remains unspecified, evidence points to it being exceptionally high, likely 8 or above, comparable to elite demons like Kalego and Balam. Opera possesses an androgynous appearance featuring long braided red hair, a straight-cut fringe, red cat-like ears atop their head, pointed elf-like ears, and a black cat-like tail. They typically wear formal attire: a red vest over a white shirt, a striped tie, and navy dress pants. As a student at Babyls Demon School, Opera had shorter black hair and wore a mix of the female uniform top and male uniform bottoms, reinforcing their ambiguous identity. Personality-wise, Opera generally maintains a reserved, stoic demeanor, acting as a voice of reason for Sullivan, though often disregarded. Beneath this professional exterior lies a mischievous and occasionally sadistic side, particularly evident with former underclassmen Naberius Kalego and Balam Shichiro. Their emotional state subtly manifests through their cat ears and tail—perked ears indicate happiness, drooping ears signal distress. Opera demonstrates deep loyalty to Sullivan and gradually develops strong protective instincts toward Iruma, despite initial skepticism about adopting a human. During their youth at Babyls, Opera was known as the "Mysterious Top Dog," secretly enforcing order by hospitalizing 666 troublemakers. Their identity remained hidden until discovered and subsequently defeated by Kalego and Balam, whom they recruited as subordinates. This history established a dynamic where Kalego maintains lingering fear and respect toward Opera. Opera's relationship with Iruma evolves significantly. Initially skeptical, they grow fond through shared experiences like training Iruma for the Execution Cannonball event. During this rigorous regimen, Opera demonstrated exceptional strength, speed, and precision, helping Iruma overcome his instinctive evasion reflexes. They participate in family activities like the Division Party, solidifying their bond. Opera is visibly disturbed when Iruma enters his "Evil Cycle" but becomes fiercely protective during crises, such as the Walter Park incident. There, they shield Iruma's friends and collaborate with Ameri Azazel to combat the Panther Rat. Opera recognizes Ameri's potential during this battle and offers her a future assistant position, intrigued by her combat abilities. Opera wields formidable combat skills: superhuman strength capable of halting demonic beasts, extreme precision in attacks, and rapid reflexes enabling acrobatic maneuvers. They command several advanced spells: La Fire for fire generation, Cherusil for object transformation, Acceleration for speed enhancement, Libera for projectile attacks, Fractal for gravity manipulation, Quan Quan for plant growth, and Gran for barrier creation. Their physical prowess is classified at Town level, with supersonic speed and Class G lifting strength. Notable details include Opera enjoying the use of beds as trampolines during laundry, hiding forks from Sullivan during disagreements, and playfully evading gender inquiries—responding to Iruma's question with "choose whatever you like." A spinoff reveals a past where Opera lived as a human street thug before becoming a bodyguard. As the Misfit Class's practical instructor, they maintain a strict teaching approach emphasizing non-magical combat training to build resilience. Opera cooks for Iruma with nurturing intent but prepares Sullivan's meals with a "work harder" mindset. Opera's development culminates in acknowledging Sullivan's wisdom in adopting Iruma, particularly after witnessing Iruma's capacity to protect others during the Walter Park crisis. They continue balancing duties to Sullivan with mentorship toward Iruma, occasionally leveraging their seniority over Kalego and Balam for tactical support or amusement.