There's Definitely Something Wrong with Cultivating Immortality in a Magical Girl's World

1v1, mainly top, gradual transformation

After transmigrating, the young Shangguan Pengcheng unexpectedly gets a System that lets him trade mana for Gu worms. He can't help but feel smug:

"I learned early that the ways of the world are hard..."

Everything comes at a price. A will in the heavens has noticed this thing that does not belong to this land.

A demon from beyond the heavens? Looks like I'll have to leave my mark on this world.

Little fox girl Shangguan Mocheng: Boohoo, why did things turn out like this?

Shangguan Moyu: Brother, you're so adorable now!

Girlfriend Xie Han: It's okay. I like you even more like this.

This is my first time writing, so the prose may not be great. Feel free to point out any issues or typos. I got so fed up with an author who never updates that I decided to write a book myself. I'm currently an intern, not a full-time writer, so updates will be slow. Please understand!