The Novel’s Masterpiece (COTE X TNE Fanfic)

Kiyotaka Ayanokouji gets an email from the author of The Returnee Hero asking for help with his novel and then later finds himself inside the world with an author intervening in his plan for a peaceful life.

Will he remain an extra or will he create the greatest masterpiece?

I do not own either of the original stories nor the art used.