Symbiote Gwen

On Earth 515, Dr. Morales and his team at Alchemax are running experiments on an alien substance known as the Symbiote. But when things go horribly wrong, Gwen is assigned to deal with it before the consequences can spread across the multiverse. But this Symbiote is not satisfied with having just one host...

This takes place in Across the Spiderverse, after Gwen is recruited and before she talks to Miles in the movie. You can even keep it as your own head canon if you want.

Contains mild smut in chapter 3 (when it comes out)