Kibutsuji no Musume

Kibutsuji no Musume is portrayed as affectionate, curious, and comfortable around the man she believes to be her father. She reacts happily when reunited with Rei and shows no indication that she considers her family situation unusual.

Her behavior is entirely that of an ordinary child. She has no knowledge of demons, the Demon Slayer Corps, or the danger posed by Muzan Kibutsuji.

When violence suddenly breaks out in Asakusa, she becomes frightened along with her mother, reinforcing how completely both have been kept unaware of Muzan's actual identity.

Kibutsuji no Musume is an ordinary human child with no established combat training, supernatural abilities, or connection to demon powers.

Nothing in canon indicates that she possesses Muzan's blood or is his biological daughter. She is the daughter of Rei, while Muzan has inserted himself into the household by posing as Rei's husband.

Kibutsuji no Musume appears during Tanjiro's first direct encounter with Muzan in Asakusa. Tanjiro Kamado follows the scent associated with the attack on his family and unexpectedly finds Muzan walking openly through a crowded street.

Tanjiro's attempt to confront him is interrupted when the girl embraces Muzan and Rei addresses him as her husband. The revelation that Muzan has constructed an ordinary human identity momentarily shocks Tanjiro.

Muzan then creates a diversion by transforming a nearby man into a demon. He escorts Rei and her daughter away from the disturbance and sends them home while claiming that he has business to attend to.

Rei is Kibutsuji no Musume's mother. The girl is openly affectionate toward her and lives with her in Asakusa.

Muzan Kibutsuji poses as the girl's father while using a human identity within Rei's household. She has no idea that he is actually a demon.

Tanjiro Kamado encounters the family while pursuing Muzan. His aggressive reaction toward the man she knows as her father confuses both the girl and Rei.