Yushiro

Yushiro is a travelling companion of Tamayo and close ally of Kamado Tanjirou. 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.

Trivia

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