"I learned long time ago that i cannot trust in or count on anyone. That why i see you so called friendship as a weakness... it invites deceit. It make you feel responsibility for other person, what opens a vulnerability that can be exploited. Count only on yourself, and belive only yourself"
— Nyx
Nyx (ニクス, Nyx) is one of first demon slayer , as a orphan child was raised by fire demon Zelodo who taught him Fire Devil Slayer Magic. Nyx is very selfish, and hate be dependent on anyone, treating everybody who get in his way as enemy, and a obstacle in his goals.
Fire Devil Slayer Magic (炎悪魔特効の魔法, Honō no Metsuaku Mahō) - Curse type Lost Magic that allow Nyx to create and eat demonic flame. Those flames are dark-orange and seem to spread darkness instead of light. Just single barerly look at his flames give a strange feeling which suggests that there is something evil and filthy in it.