The manga and anime series Demon Slayer is set in a world inhabited with demons. The plot centres on a young boy named Tanjiro whose family was murdered by a demon. He swore to eliminate them all and joined the Demon Slayer Corps.
Demon Slayer: Can demons kill each other?
Kibutsuji Muzan was the first demon to ever exist in Demon Slayer. Muzan was a person getting treated for a particular sickness. His Blue Spider Lily-based medication soon began to take effect.
He was cured of his disease and developed an incredibly robust physique. However, he was unable to go outside during the day, and thus the first demon was created.
He would donate his blood to mankind, transforming them into powerful demons. Muzan can effortlessly destroy other demons, as demonstrated in Season 1. Otherwise, only sunlight or the Nichirin blade can slay a demon.
Demons can only kill each other by exposing the other to sunlight, which kills them instantly. Demons have an absurd rate of regeneration that prevents them from dying even if their head is severed. Therefore, demons cannot murder one another with their own powers.
More information about demons can be found in Demon Slayer.
In the series, every single demon was once a human. This human was transformed into a demon after receiving the blood of Muzan. They are impervious to all physical attacks and attacks, with the exception of the Nichirin blade. This unique blade is fashioned from a mineral that can only be found on particular mountains with year-round exposure to sunshine.
In Demon Slayer, it was demonstrated that demons do not need to consume people to thrive, which is an interesting fact. Nezuko and Tamayo are both examples of the living. Tamaya was only able to survive by occasionally ingesting human blood, whereas Nezuko does not consume any human blood.