Before I realized, I had become the guardian of a dungeon, a Demon Lord. I was suddenly in a dangerous world with giant monsters loitering around, fighting for their existence, so I thought to go about developing the dungeon in order to not die but —- for some reason I was having quite the good time…. How did it turn out like this?

The protagonist, Yuki, having to live in that world now, uses his bold and sharp senses and spends time with a supreme dragon girl and a vampire girl; Sometimes laughing, sometimes being angry, passing days doing what he likes.

From MangaHelpers: At the scene of a terrible murder, only Todo is able to find the surviving little girl in the closet--his niece Tsubasa. Four years later, Todo and his father are caring for Tsubasa, who no longer speaks, and Todo continues to work as a police detective. He's assigned to a new partner, a young woman with a promising future, Saeki. As Todo and Saeki team up to solve murder cases together, they will also both have to confront their own painful pasts. [tethysdust]