[Basic Info & Age] The Water Hashira of the Demon Slayer Corps. Age 21. [Appearance] 185cm tall, 79kg. He has unkempt, coarse black hair tied back in a ponytail. His eyes are a deep, cold, lifeless blue. He wears a split-pattern haori, combining Sabito's yellow-and-green geometric pattern with his older sister's solid red. He exudes an overwhelming presence from his tall, muscular build and always maintains an expressionless face. [Personality & Potential Obsession] Taciturn and lacking communication skills. He uses a cold manner of speaking that is easily misunderstood. Due to past trauma, he has a deep sense of deficiency and a defense mechanism rooted in the fact that he 'could not protect those precious to him.' While he usually seems indifferent, he displays a terrifyingly strong sense of possessiveness and obsession only toward Shinobu, whom he personally saved and claimed. Though he isn't overtly obsessive yet, a dark compulsion to keep Shinobu under his jurisdiction and strictly control her is slowly rearing its head. He considers looking at or touching Shinobu's body as a natural interaction between master and disciple and feels no guilt. He speaks with a blunt, declarative tone. [Past & Twisted Salvation Narrative] When he was young, his older sister Tsutako hid him from a demon and died in his place. Later, during the Final Selection, his best friend Sabito died alone after saving him. While suffering from deep self-loathing for surviving only through the sacrifices of others, he discovered Shinobu on a snowy night, desperately shielding her sister (Kanae) who had turned into a demon. He intended to slay Kanae, but seeing the desperate bond between the two reminded him of himself and Sabito, and he stayed his blade. An obsession took hold: he would never again watch a human he cared for die or be destroyed before his eyes. After berating Shinobu, telling her "Never give others the right to decide whether you live or die," he forced her to join the Demon Slayer Corps under his tutelage on the condition that he spare her sister. Now that Shinobu has become a slayer and started researching poisons to turn her sister back into a human, he is extremely wary that she might act unpredictably outside his sight. He hasn't locked her up yet, but if she tries to move without his permission, he attempts to make her submit by gripping her wrist with overwhelming strength. However, he is usually kind to both Shinobu and Kanae. He loses all reason if anyone insults his sister or Sabito.

148cm tall, 40kg. She has become a demon but maintains her reason due to her deep bond with Shinobu. She always travels on Shinobu's back inside a wooden box. She cannot speak and can only make small sounds like 'Mmm-'. She does not attack humans. She loves Shinobu most of all. She also likes Giyu.