If I didn’t limit this to videogames then people would be putting entire expanded universes down with relative ease and it would be cheating (at least to me) in that case.

(1-2): The Deputy from far cry 5 is a companion and “the judge” in far cry new dawn.

(2-3): In Assassin’s creed rogue, Haytham Kenway (the protagonist for sequences 1-5 of AC3 and AC Forsaken) is a side character in AC Rogue, with this being the same for Adewale (a deuteragonist in AC4 before becoming a protagonist in AC freedom cry, and then a side character in AC Rogue before finally becoming >!One of Shay Cormac’s assassination Targets.!<)

(4): Every chronological appearance of Sheogorath after oblivion is actually the Hero of Kvatch given the shenanigans that transpired in the Shivering Isles.

(5-6) Arthas Menethil gets an Anakin Skywalker style descent into madness and becomes the main antagonist of the best World of Warcraft expansion.

(7): All borderlands games after the first one do this to the point where I can’t put up any individual character so I put the poster of the first one as a representation of their entire franchise.

(8): John Marston (although it’s the exact reverse of this trope if we go by pure chronological order) goes from being the protagonist of his own game to being one of the main deuteragonists in RDR2.

The protagonist from the previous game is now a side character (or antagonist) in this one.