I actually have one I’ve adapted from a holiday SessKag fanfic (To Bargain with the Demon) into an OG of the same title. I write under the pseudonym of Enola M. Douglas, and the ebook is currently available on Amazon. It is short and sweet and a holiday romance, perfect for the season.
Tomorrow, Dec 11, the ebook is scheduled to be free, though it’s always ‘free’ if you have Kindle Unlimited.

I am working on adapting my bigger works into OG as well (First Comes Marriage, You & Me After All, and eventually The Way to Elysium), but the holiday tale was a small and fun one to try to adapt!

Anyway, thanks for the ask and good luck on your search!

I was wondering if there are any books that may have started as Sess/Kag fanfic.
The only one I can think of is Tsumiko and the Enslaved Fox, but I would love to hear other suggestions.

Danyealle-sama writes as Danyealle Autumn Myst and has redone some of her fanfics as originals. Some of her novels are on Amazon if you search for her pseudonym.

Thank you!