Genkai Dungeon no Hanshoku Jijou

Egin is the boss of a dungeon where heroes have hunted out all the monsters. In order to revive the dungeon, where there is now a 100% chance of reaching the boss's room, Egin and Saille (a virgin unicorn and his second in command) tackle trying to breed more monsters. But the dungeon's monsters are hard to deal with... such as complicated slimes that have fallen in love with humans, and a shy Dullahan. Will Egin really ever be able to revive the dungeon?

(Source: Kadokawa, translated)