O (джен)

Steve Rogers met Bucky Barnes on his first day at West Point. Since then, Steve harboured an unrequited love for the most brilliant man in the world. However, Steve knew that Bucky was still in love with a man of his past... someone Steve could never hope to replace in Bucky's heart.
One day, a special mission went terribly wrong as they were both captured by an unknown enemy only to be rescued by an organization called SHIELD. As Steve fights against a terrible enemy that threatens to destroy all of humanity, he starts to uncover the secrets of Bucky's heart... as well as of the future.
Or...
The Tenet AU where Steve is the Protagonist and Bucky is Neil.
This is a Tenet AU, so it will contain spoilers for the movie.