Yushiro

Yushiro is a travelling companion of Tamayo and close ally of Kamado Tanjiro. He was turned into a Demon by Tamayo.

History
Yushiro was human who was under the care of Tamayo as she was practicing as a medical practitioner. He was in frail state fighting a disease when Tamayo gave him the choice of succumbing to his illness or to live longer as a demon. He agreed to become a demon and has since stayed by Tamayo's side serving as an assistant as well as her guard.

Tamayo
Yushiro is in love with Tamayo and is willing to do anything to protect her. He finds Tamayo very beautiful. He is very obsessed with her and will attack and insult anyone who comes near her but him.

Trivia

 * If someone tells Yushiro "You like Tamayo-san, don't you!", he gets super red and quiet.