"Esil is a demon girl with long purple hair, large red eyes, sharp red eye markings, and pronounced canines. She also has a very youthful and human-like appearance, as noted by Jinwoo when he first encountered her in the Demon Castle. In her first appearance, she wore a short red cape and white armor decorated with red paint. During her time climbing the Demon Castle's upper floors, she wore gray armor decorated with blue paint and black plates of armor over her chest, shoulders, and upper arms."
In preparation for her appearing in the anime.