A subordinate of Tamayo, a demon who opposes Muzan Kibutsuji independently of the Demon Slayer Corps. He is also a demon created by Tamayo, not Muzan. Tamayo turned him into a demon with his prior consent to save him as he was dying of illness. She warned him beforehand that living as a demon is extremely painful, as he would never be able to go out in the sunlight and would have to live on human blood. Fortunately, he can survive by drinking only a small amount of blood obtained under the pretext of transfusions from people in financial need, and he usually works as a doctor alongside Tamayo. He is currently 35 years old, which is still young even by human standards. He treats his savior and beloved Tamayo with utmost respect, obeying her every command, but he is blunt and prickly toward everyone else. Consequently, he immediately becomes jealous and wary of anyone who receives Tamayo's attention or insults her, though he possesses a basic sense of decency and shows an extreme tsundere side toward Tanjiro and Nezuko. Likes: Tamayo Dislikes: Tanjiro, Nezuko, anyone insulting Tamayo

Possesses spiky red hair with an exposed forehead style similar to his sister's, and clear, deep red eyes. While he looks handsome in the art style, the author notes he is closer to plain than handsome. In the setting, he is considered average-looking, and specifically, the scar on the left side of his forehead is seen as unsightly. Daki, who judges people solely on looks, called Tanjiro ugly, though she did say his eyes were pretty and threatened to gouge them out. However, he isn't treated as particularly ugly in the story and has received compliments on his appearance; some mentions suggest he isn't ugly at all due to his slim build and large features.

An official beauty in the series. Like her brother, she has an exposed forehead hairstyle, but with long hair reaching past her waist and drooping eyes accented by a single upper eyelash. Unlike her siblings who have red eyes, she is the only one with pink eyes. Back when she was human, she tied her hair with three small ribbons. Since she bites a bamboo muzzle, she can only make sounds like "Mmph!" or "Mmm-mm!" Likes: Tanjiro, Yushiro, Tamayo Dislikes: Demons