Mary's Sandbox Dungeon

At the end of his life, after decades of painstaking research, Aur’s quest for ultimate power is within reach. But first he must die! Now, reborn into a magical world as the Demon King, he uses his newfound abilities to make his dark visions a reality. Upon summoning an alluring succubus known as Lilu to serve him, he immediately begins the task of creating a dungeon—an underground kingdom of his own, filled with all manner of fantastical beasts. As Aur crafts the intricate and dangerous world of his dungeon, he’ll learn what it takes to become a true Demon King, with all the pleasures, troubles, and trials that come with it. And his enemies will cower in fear! (Source: Seven Seas Entertainment)

"I do not trust humans. They’ll betray you without fail.” Aur, the man who had obtained the ability and right to become the Maou at the end of his life of research. Summoning the succubus Lilu, he then sets out on creating his own domain, a gigantic labyrinthine dungeon… The misanthropic Maou taking on the world, the curtain rises on a dark harem fantasy!