Hey hey
I ADORE this couple. They're definitely my favorite alt! pairing. I wish more people would write them, I think they have an interesting dynamic.
Anyway, some other fics I haven't seen mentioned:
Like Charity's "passion is accurate" fantastic early Effily fic. Effy here is particularly brilliant.
likecharity: passion is accurate, effy/emily, nc-17
readyfortiger's Harder than Me, which kind of flips the usual paradigm of Effy/Emily relations.
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They're both very smutty, unfortunately I can't think of many other fics besdes Trans that really expands on what they would be as couple. Unlike Naomi/Katie, Naomi/Effy and Katie/Effy which are fairly popular alt pairings.
Hope you like them!