A Demon Lord's Tale: Dungeons, Monster Girls, and Heartwarming Bliss

A Demon Lord's Tale: Dungeons, Monster Girls, and Heartwarming Bliss summary:

One day, I woke up only find out that I’d become a Demon Lord, an individual responsible for protecting a dungeon. The world I’d been spirited away to was one filled with violence. Gigantic monsters wandered through it and competed with each other each and every day for the right to survive. I had no choice but to strengthen my dungeon’s defenses in hopes of living another day—or at least that was what I’d thought. For some odd reason, I instead ended up spending my days in relaxation and bliss.
This is Yuki’s story, my story. It tells the tale of how I spent my days after settling down in a dungeon with a self indulgent, “supreme” dragon girl and a young vampire.