Esil Radiru is a demon noble and a princess of the Radiru clan.
Esil is a young demon girl with long purple hair, large red eyes, sharp red eye markings, pronounced canines, and a slender build. 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 with Jinwoo, she wore gray armor decorated with blue paint and black plates of armor over her chest, shoulders, and upper arms.
Despite being a demon, Esil has an open, honest, and affable personality. She is also somewhat selfish and shameless, as displayed when she had no problem begging for her life after all of her knights had been mercilessly killed by Jinwoo.
When Jin-Woo made it to the 80th floor of the Demon Castle, Esil and several of her clan's knights were sent out to eliminate him and his shadow soldiers. They made easy work of Tank's team, but doing so led Jin-Woo right to them. After she watched him easily slaughter her knights and then slice her spear in half, Esil surrendered and begged for mercy, claiming that she would do anything he asked if he spared her life. Somewhat amused by her personality and not really willing to kill her due to her human-like appearance, Jin-Woo accepted her deal and she led him to her clan's castle, where he was given the entry permit that he needed to move to the next floor.
As part of her deal, Esil accompanied Jin-Woo as he ascended the castle, watching in awe as he effortlessly slaughtered the inhabitants of each floor. Upon arriving on the 100th and final floor, they were attacked by Baran, the Demon King. When Baran eventually got the upper hand on Jin-Woo, Esil distracted the Monarch by throwing a dagger at his face, giving Jin-Woo an opening and allowing him to finally kill Baran with a powerful punch to the jaw.
In the aftermath of the battle with Baran, Esil watched as Jin-Woo crafted the Holy Water of Life and extracted Kaisellin's shadow from its corpse to add to his army. Delighted that her clan was now the top-ranking clan in the castle, she then asked Jin-Woo if he could return to the 80th floor to have a grand feast with the Radiru clan, but he declined, citing that the 80th floor was too far away. With no reason left to stay and eager to see if the Holy Water of Life would be able to cure his mother of Eternal Slumber, Jin-Woo bid Esil farewell and before she could say anything else, he disappeared by using Shadow Exchange.
As a demon noble, Esil is strong for her species and the very least, measures up to a S-Rank in fighting ability. While briefly dueling Jin-Woo with her spear, she was also able to rip large holes in a building behind him and accurately aim for his weak spots.