Dungeon Builder: The Demon King's Labyrinth is a Modern City! (Manga) Vol. 8

A mastermind's shadow looms overhead, and Procel intends to thwart any malicious plans! After saving Marco from near death, Procel swears to always be with her. As he enjoys a peaceful life for the first time in a long while, Stolas, the Demon Lord of Wind, faces her first war against a rookie demon lord. Unbeknownst to her, a trap awaits! When Procel attempts to join her battle, Stolas opposes: "This is my war and I'm going to win this on my own!"