Dungeon Builder: The Demon King's Labyrinth Is a Modern City! (Manga) Vol. 6 (manga)

After obtaining a forbidden power, Procel learns of a senior demon lord’s plot against him. Unwilling to let another lord belittle his townspeople or force them to submit to outside rule, Procel plans a counterstrike against the oppressive neighboring town, Eklava. But as fear and despair grow, so too does Procel’s untapped power as a demon lord. When that growing power puts his best friend Marco at risk, more fire power will be needed to beat back Eklava and its oppressive demon lord!