Apparently this is one.
https://chooseyourstory.com/story/fear-the-psyker
I'm not familiar enough with the franchise.
Oddly I was thinking about doing some book reviews involving warhammer recently.
If you like minis I have your back
Fear The Psyker is a great read, but I think that is one of the only 40k fanfic there is on the site. If you're looking to get into some 40k books for inspiration, let me know. It's about the only thing I've been reading in the past year.
Ooo, looks like I'll be checking it out. Hopefully the 40k words is coincidence and not random shit to be cool.