Dungeon no Aru Sekai de Kashikoku Sukoyaka ni Ikiru Houhouダンジョンのある世界で賢く健やかに生きる方法（コミック）; How to Live Wisely and Healthily in a World with Dungeons

Ten years ago, dungeons suddenly appeared all over the world. Yuma Minashiro fell into a dungeon on his way to a job interview. With no equipment and resigned to his death, Yuma obtained an incredible skill: summoning. It was tough because all the spirits he summoned were beautiful girls, and the only way to become stronger was to flirt with them, but he set up a company, made money, and lived a happy life as a dungeon explorer.