In Rainbow Rowell's Fangirl, Cath is a Simon Snow fan. Okay, the whole world is a Simon Snow fan, but for Cath, being a fan is her life--and she's really good at it. She and her twin sister, Wren, ensconced themselves in the Simon Snow series when they were just kids; it's what got them through their mother leaving.
A masterpost of recommendations for fanfic, S4 or otherwise. Cannibal Club authors are highly encouraged to link their work here. [more inside]
Adventure Time: The Prince Who Wanted Everything Season 6, Ep 9
Lumpy Space Princess kidnaps the Ice King and forces him to read her self-insert fanfiction set in the world of Fionna and Cake.