>>11363270
Couple of my favorite long form weight gain stories:
>"Fuck America" by Dania201
https://www.deviantart.com/dania201/art/F-ck-America-Chapters-1-2-887402425

>"Aiko's Growth" by Swuffed (original upload was taken down, PDFs reuploaded by me)
https://gofile.io/d/Z0RK7i

If you aren't looking for weight gain specifically, I'd also recommend "Long Road to Hyrule Castle" by PinkRei

https://archiveofourown.org/works/63236689