Dungeon Builder: The Demon King's Labyrinth is a Modern City! Volume 9 features story by Rui Tsukiyo and art by Hideaki Yoshikawa.

When Balam, the Demon Lord of Darkness, reveals he had been pulling strings in Stolas’s war and requests a collaboration, Procel launches on a mission to rid himself of the troubling Demon Lord. Why, what better way to deter the Demon Lord of Darkness than by filling his own city with light? As his countermeasure against Balam, Procel begins his city’s newest project--a casino! Can his city full of smiles deter a surly fellow demon lord?