Even if I hate him ingame for me it’s gotta be Genji.
But that might also be because I love stealth games so I am really biased towards stealthy characters (ofcourse he isnt really stealthy ingame but he literally is a cyber-ninja).
A singleplayer game would also allow for a in depth talent tree since now they only gotta worry about one character + PVE balance can be a bit OP.
As far as I know singleplayer games aren’t really blizzards thing though which is kind of a shame. I think PVE in general would have been much better as its own game so you dont have to worry about balancing issues.
I mean reworking a hero when that hero also has a talent tree sounds like a nightmare to me.
Sigma, it could end up being a psychological puzzle game, think of something from the devs of inscryption.
Bonus: add sombra to it as a sort of “Easter egg” leaving trails of his past and bits hidden across the games. Reason - I think she secretly cares for him and wants him to break loose in some ways.