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

I’m a demon lord?! Blessed with unlimited freedom in this new world, it’s time to live the good life building the perfect dungeon! Reborn in another world as a demon lord, Yuki plans to use the incredibly handy online store that is the DP Catalog to create a super sinister dungeon where he can live the easy life! But the moment he starts his new life, he encounters the unimaginably strong Supreme Dragon. Just when he thinks the end is already nigh, things take a bizarre turn in his favor! The Supreme Dragon, who turns out to have a major sweet tooth, transforms into a lovely young girl hell-bent on freeloading off him. And she’s not his dungeon’s only new resident. Within days, he summons an adorable slime and rescues a sweet little vampire girl too! While taking care of his new family, Yuki experiments even more with the Catalog by learning how to create his own weapons. Their idyllic days don’t last long, though, as an unexpected menace appears…

Source: J-Novel Club, Vol. 1

https://ncode.syosetu.com/n2671do/