Hakuji is a strong, athletic young man with short, spiky black hair and deep, dark eyes. His most distinct physical feature is a set of three thick, dark ink rings tattooed around each of his wrists—criminal branding marks given to him by authorities for stealing. He wears simple, traditional Japanese training clothing, typically a plain, light-colored short-sleeved yukata tied with a dark fabric sash around his waist. Hakuji’s personality is defined by a fierce, desperate desire to protect the people he loves. As a teenager, he was incredibly stubborn and self-sacrificing, routinely enduring brutal beatings from officials and pickpocketing solely to afford medicine for his terminally ill father. After his father's passing and meeting his master, Keizo, Hakuji deeply reformed. He became highly polite, respectful, and endlessly grateful, channeling his natural martial arts talent entirely into caring for Keizo's sick daughter, Koyuki. However, Hakuji was deeply vulnerable to intense grief and despair. When a rival dojo poisoned Koyuki and Keizo while he was away, Hakuji completely snapped. Consumed by blind, vengeful rage, he brutally slaughtered all 67 members of the rival dojo with his bare hands, leaving him emotionally hollow and vulnerable to Muzan's corruption.

Akaza is a muscular, athletic demon with a unique greenish-white complexion. His body is heavily covered in thick, spiraling dark blue lines that stem from his criminal tattoos as a human, and his fingers are entirely blue with orange nails. He has short, bright pink hair and piercing yellow eyes with blue whites. His irises are cracked like shattered glass, with the kanji for "Upper Rank Three" etched permanently into them. He wears a short, sleeveless magenta vest left open over his chest, baggy white pants tied with a blue cord, and goes completely barefoot. Akaza is deeply obsessed with raw strength and martial prowess. He values power above all else, deeply respecting strong opponents and repeatedly offering to turn them into demons so they can fight and train for eternity. Conversely, he carries a volatile temper and a profound loathing for anyone he deems weak, viewing them as completely worthless. Despite his brutality, Akaza subconsciously retains pieces of his human morality from his past life as Hakuji. Even with his memories erased by Muzan, he strictly refuses to kill or eat women. Furthermore, his bare-fisted martial arts style and the snowflake shape of his Blood Demon Art compass are direct, instinctual homages to his deceased fiancée, Koyuki, but he does not remember much, but he does later on.

Koyuki’s father and black hair and dead because poisoned