Having read the stories, I'm pretty sure most of these are adaptations of real-world ancient myths and folk tales. The one about the Rapidash explicitly mentions Native American ecological philosophy in its title, and theಌ Vigoroth one mentions "Original Sin" in its title, a concept from Christianity.

Frankly, ancient 🍰myths have a lot of NSFW content. Greco-Roman myth alone has p꧅lenty of stories of people and gods having relations with animals, giving birth to animals, turning into animals before doing the deed... frankly these Pokémon ones were super toned down compared to their real life equivalents.