You can choose from Mei, Genji, and Bastion - yes, you can romance everyone's favorite walking turret (who communicates in full on R2-D2 esque beeps and boops).
The game's been under development since the beta ended, and reportedly is already 180,000 words long including all three paths in the game - longer than I think there might be a bit of dashed expectations between the players and the game, because new people come to the blog and they think that every one of the 21 heroes is going to be in it.
I expect it less from Blizzard if the content isn’t objectionable.
Because I know the people who made [the] Starcraft 2 visual novel, and Blizzard okayed that.
and can choose from three paths at the beginning of the game based on your profession (for example, a player can choose to be an Oceanographer and partner with Mei).
These paths determine your partner for the game, and will allow you to romance them throughout the course of the game.
But I guess that’s always kind of a concern in the back of our minds, because we’ve spent quite a while on it now.