Maou-sama no Bugtrap Dungeon Seisakuki

The Demon King was defeated, and peace was restored to the world. It's that sort of world that the adventurers rush around in... However, the Demon King has not perished! Having obtained the mysterious power "Bug"—neither magic nor skill—the Demon King lurks in the deepest recesses of the dungeon with a few confidants, sharpening his fangs for revenge! Using the deviant power of "Bug," he sets invisible traps in the dungeon, aiming to expand his army by transmogrifying adventurers into demons!

(Source: Mag Garden, translated)