Maou ni Natta node, Dungeon Tsukutte Jingai Musume to Honobono Suru

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?