Dungeon Battle Royale: Maou ni Natta node Sekai Touitsu wo Mezashimasu

In the year 20XX, God put the "World Salvation Project," into motion to save humanity from heading towards its destruction. As a result, Shion Kurosaki, a college student who continued to struggle in a broken world, was picked to be the demon king. As he repels the self-proclaimed hero as she leads the raid on his dungeon, a war for supremacy between the demon lords unfold?!

(Source: Hifumishobo, translated)