HHG and many other games use Koikatsu to make their visuals, from character models to backgrounds.
There's a lot of assets in there made by a larger community that are free to use and because of that you'll see a lot of developers using the same assets to convey totally different stories.
Also random fact.
CK came out first, it has been in development for 2 years now but it was only published to itch.io a few days ago.