'...he smiled, apparently amused. “The apocalypse seems to make for strange bedfellows. A Sokovian Baron and a Winter Soldier walk into a bar.”'
Due to the current vastness of the Marvel Cinematic Universe (MCU - the Marvel movies) sometimes it can be difficult to explain where, within the sprawling fandom and its sub-fandoms, fan-created content fits in.
This week's fic is mostly based on the Marvel's What If..? zombies episode, but also reaches into the main continuity, and hoiks out Zemo, dropping him into the zombie-ness so that he can play too.
While Zemo was present in Captain America: Civil War, he really came into his
own in The Falcon and The Winter Soldier (TFATWS.) Civil War
has happened in this universe (or at least, the fic author presumes,)
but TFATWS hasn't.