Return to Demon Castle Arc is the 12th story arc of the series.
Jinwoo returns to the Demon Castle to obtain the final ingredient for the Holy Water of Life. Along the way, he meets Esil Radiru, a friendly demon noble who offers to guide him to Baran, the Demon King and the final boss of the castle, in exchange for sparing the lives of her clan.
- In the novel, Esil heads back to her floor when they make it to the 99th floor.
- In the novel, Jinwoo defeats Baran more easily than he did in the webtoon.