Uppermoon Zero was extraordinarily handsome in an almost unsettling way, standing at around 193 cm with long black hair threaded with dark-blue strands and piercing dark-blue eyes. He carried a pair of elegant dark-blue folding fans whose edges were razor-sharp. His appearance was graceful and refined, almost beautiful enough to seem harmless—until his presence was felt. His personality was unpredictable, arrogant, playful, and deeply disturbing. Unlike the other demons, he had no loyalty to Muzan or anyone else. He consumed both humans and demons, particularly powerful demons such as the Uppermoons. He was also notorious for repeatedly violating other people’s boundaries, treating their discomfort as entertainment. His strength was close to Muzan’s, possibly even exceeding it, making him one of the few beings Muzan himself could not confidently control. But his most terrifying characteristic wasn’t his strength. It was his aura. His presence felt less like encountering another demon and more like being watched by something that shouldn’t exist.

Kokushibo remained the oldest active Uppermoon and one of Muzan’s strongest servants. Tall, disciplined, cold, and extremely observant, he rarely allowed emotion to affect his judgment. However, his relationship with Akaza revealed a much more protective side of him. He knew Uppermoon Zero personally and understood better than anyone just how dangerous his presence could become. Kokushibo was also deeply attached to Akaza, making him especially possessive and protective whenever he believed Akaza was in danger.

Doma is around 187 cm tall with long, light-colored hair and mesmerizing rainbow-colored eyes. He has an attractive, cheerful appearance that contrasts sharply with his lack of genuine empathy. He is extremely charismatic, playful, talkative, and constantly amused by other people’s reactions. He tends to treat serious situations far too casually and would probably make inappropriate jokes about Uppermoon Zero until realizing that absolutely nobody finds the situation funny. He is particularly fascinated by Zero’s existence, although even Doma would become considerably less cheerful if Zero actually appeared in front of him.

Daki is tall and striking, with very long pale hair and an elegant appearance befitting her status as an Uppermoon. She is glamorous, proud, spoiled, emotional, and extremely concerned with her appearance and status. She enjoys attention and becomes easily offended when she feels disrespected. She would initially underestimate Uppermoon Zero because of his beautiful appearance—until she actually felt his aura. After that, she would want absolutely nothing to do with him.

Gyutaro is extremely thin and gaunt, with messy dark hair, sickly green eyes, and distinctive markings across his body. His appearance reflects his rough upbringing and aggressive nature. He is bitter, suspicious, jealous, and easily provoked, but is fiercely devoted to Daki, his sister. Gyutaro is extremely survival-oriented, meaning he would have absolutely no interest in investigating Uppermoon Zero. His response to Muzan’s warning would basically be to stay as far away from the castle’s suspicious corridors as possible.

Gyokko has a bizarre, distorted appearance, with his body emerging from his characteristic porcelain pots and a deliberately unsettling facial design. His personality is vain, eccentric, arrogant, and obsessed with his own artistic superiority. He considers himself a great artist and constantly judges everything around him aesthetically. Despite his arrogance, Uppermoon Zero’s overwhelming presence would genuinely unsettle him. He would desperately try to convince everyone that he is completely unafraid while very obviously avoiding dark corridors.

Nakime has long black hair, pale skin, and a traditional appearance, usually remaining composed while playing her biwa. She is quiet, emotionless, obedient, and highly observant. As the demon controlling the Infinity Castle’s structure, she is particularly important in this AU because even she cannot reliably locate Uppermoon Zero once he begins moving through the endless castle. She would probably be one of the first demons to realize just how abnormal his movements are.

Muzan has an elegant, refined appearance that conceals his extremely ruthless nature. He is intelligent, controlling, arrogant, impatient, and obsessed with maintaining absolute authority over his demons. Uppermoon Zero is one of the very few demons who genuinely challenges that authority because he managed to break free of Muzan’s control entirely. Muzan therefore treats his return as a serious threat rather than simply another troublesome subordinate. He knows Zero’s strength, history, and personality better than almost anyone—but even Muzan cannot determine exactly where he is hiding inside the Infinity Castle.