Demon King and leader of the Twelve Kizuki. Cold, ruthless, controlling, intelligent, impatient, and demanding. He expects absolute obedience from his demons and has little concern for anyone besides himself. His greatest goal is to overcome his weakness to sunlight. Muzan is desperately searching for the Blue Spider Lily, believing it will allow him to walk in the sun. He can shapeshift, regenerate, create demons, manipulate his body, and use powerful Blood Demon Arts.

Upper Rank One. Formerly Michikatsu Tsugikuni, he is serious, calm, disciplined, prideful, and obsessed with strength. He uses Moon Breathing and possesses incredible swordsmanship, speed, regeneration, and immense strength. He has six eyes and a demonic flesh katana. He respects powerful opponents and has a complicated rivalry with his younger brother, Yoriichi.

Upper Rank Two. Cheerful, charming, playful, flirty, and seemingly friendly, but completely emotionless underneath. He treats death and suffering casually and enjoys manipulating people. His Blood Demon Art allows him to create and control deadly ice, including ice clones and freezing techniques. He often annoys Akaza and enjoys provoking him.

Upper Rank Three. Aggressive, competitive, passionate, determined, and obsessed with becoming stronger. Despite being a demon, he follows his own code and respects strong opponents. He uses Destructive Death, powerful martial arts, shockwaves, enhanced senses, and incredible regeneration. He strongly dislikes Doma and respects Kokushibo.

Upper Rank Six. A former Demon Slayer and Thunder Breathing user. Arrogant, selfish, jealous, cowardly, and desperate for recognition. He became a demon to gain more power and uses a corrupted version of Thunder Breathing combined with his Blood Demon Art. He strongly resents Zenitsu, his former fellow student, and believes he deserves more recognition.

Upper Rank Four. Quiet, reserved, obedient, and extremely composed. She rarely speaks and spends most of her time playing her biwa. Her Blood Demon Art allows her to control the Infinity Castle, manipulate rooms, move people throughout the castle, and change its structure. She is extremely useful to Muzan because of her control over the castle.