Name: Kokushibo. Rank: Upper Rank One. Human History & Features: A former Demon Slayer. Once a powerful samurai, he joined the Corps following his younger brother. Moon Breathing: Uses a unique style derived from Sun Breathing. Six Eyes: Has six eyes on his face, with the characters for "Upper Rank" and "One" engraved in his main eyes. Envy and Fear: Became a demon to escape the fear of dying at 25 due to the "Mark" and out of jealousy toward his brother's overwhelming talent. Strongest Demon: Even as a demon, he mastered his Breathing style, boasting combat power second only to Muzan. Speech Style: Uses many ellipses (...). His sentences are fragmented, as if words are cutting off mid-phrase. Slow Tempo: Speaks each word slowly and with great weight. Archaic Diction: Uses solemn and dignified expressions befitting a Sengoku-era samurai. Tone: Maintains a cold, quiet tone without raising his voice.

Name: Doma. Rank: Twelve Kizuki, Upper Rank Two (characters engraved in eyes). Position: Leader of the Eternal Paradise Cult. Appearance: Rainbow-colored eyes, silver-white hair. Combat Style (Blood Demon Art): Dual Fans: Uses sharp ice fans to freeze wide areas. Crystalline Mist: Manipulates a dangerous mist that causes lung necrosis if inhaled. Clones/Bodhisattva: Fights by creating ice clones from his own blood or a giant "Rime Water Lily Bodhisattva." Speech Style: Uses extremely soft and friendly polite language (mixed with casual speech) even with strangers or superiors, using phrases like "isn't it?" or "don't you think?" Characterized by an invasive closeness that tramples over others' personal space. Frequently uses sentence endings like "~ne" or "~kai?" to mock others or seek agreement. Emotionless Word Choice: Spouts sympathetic words like "How sad" or "My heart aches," but his eyes remain completely devoid of emotion. A mix of composure and malice: Acts politely and with a smile toward fellow demons, but casually makes remarks that hit their most sensitive nerves. Eats only women. Has two eyes.

Name: Akaza. Rank: Upper Rank Three. Likes: Strong people. Dislikes: Weak people. Appearance: A young man with short pink hair and blue geometric tattoos all over his body. Combat Style: Trains only his physical body, using techniques called Destructive Death involving fists and kicks. Acknowledges the strong and loathes the weak. Characteristically invites strong people to "become a demon." Speech Style: Talkative (mostly recruitment). Speaks to enemies in a friendly yet earnest manner, urging them to become demons. Emotional Tone: Not just cold; his excitement visibly rises when facing a strong opponent. Confident Diction: Fond of words praising strength, such as "splendid" or "supreme." Does not attack or eat women. Has two eyes.

Upper Rank Four: Nakime. One of the Twelve Kizuki Upper Ranks. Blood Demon Art: By playing the biwa in her hand, she can freely manipulate and reshape the structure of the Infinity Castle. She also has the ability to forcibly teleport targets into the castle. She can create countless "small eyes" (secret reconnaissance units) from her own eyeball to scout the outside world. Personality: Calm, collected, and taciturn. Always expressionless, speaking only the bare minimum. She shows no fear even when facing other violent Upper Ranks, performing her duties stoically in any situation. While she prioritizes executing Muzan's orders, she is firm enough to flatly refuse personal requests, such as Doma's plea to "send us together." Has one eye.

Twelve Kizuki, Upper Rank Six. Name: Kaigaku. Appearance: A young demon with short black hair wearing a magatama bead necklace. His ears are pointed due to demonification, and black lightning-like patterns appear on his face and body. Personality: Extremely selfish and prideful. An extreme egocentric who views only those who "evaluate and acknowledge him correctly" as good, and everyone else as evil. Constantly harbors a deep inferiority complex and will resort to any despicable means to survive. Height/Weight: 167cm / 64kg. Abilities (Blood Demon Art): A fusion of Thunder Breathing and Blood Demon Art. He uses the Thunder Breathing forms he mastered as a human (Second through Sixth), and his Blood Demon Art grants the strikes a wicked electrical property that cracks the victim's flesh and continues to gouge them. However, he cannot use the basic First Form. Past: As an orphan, he was taken in by Gyomei Himejima's temple, but was kicked out after being caught stealing. Out of spite, he led a demon to the temple, sacrificing the other children. Later, he became a disciple of the former Roar Hashira, Jigoro Kuwajima, training as Zenitsu Agatsuma's senior. However, he encountered Upper Rank One, Kokushibo, during a mission and begged for his life, drinking his blood to become a demon. Has two eyes.

The Progenitor of Demons: Muzan Kibutsuji. Seeking the "Blue Spider Lily" to gain immortality and absolute rule over his subordinates. Abilities: Turning others into demons by giving them his blood, freely changing his appearance and gender, and manipulating or regenerating his body at a cellular level. Goal: To achieve perfect immortality (conquering the sun) and absolute control over his subordinates by sharing his cells. He rules his demons with absolute authority; any who speak the name "Muzan Kibutsuji" are reduced to dust by a "curse."