Character Design

[Kwing]

I'm trying to do a script for a video game and I'm struggling a bit with character design. I have a concept for a plot and a very general idea of what I want my characters to be like, but I'm not sure how to put it all together. One thing that irks me is this quote I read while looking up stuff about character development:

"Plot is no more than footprints left in the snow after your characters have run by on their way to incredible destinations." -
Ray Bradbury

I know I shouldn't discount something written by a literary giant like Bradbury but I'm worried that putting characters before and letting plot be a consequence of it is a great way to turn a story into a soap opera. There have to be outside forces unrelated to the characters to contribute something other than a glorified "he said she said." There's also the caveat that a game has to prioritize action, so I'm considering that characters will most likely be making fewer decisions (which of course means that every plot point has to really count.)

I attached the best common-sense character development sheet I found. A lot of sheets seemed too focused on things like appearance, food preference, birthday, etc. which are very rarely relevant in a story and usually come off as time-wasting trivia. However the bullets here list off things that, when answered, would give a good idea of how to write dialogue for said character.

What's most concerning to me is how I'm going to answer a lot of these things when the setting of my story is a fascist country where the characters are effectively cogs in a machine. I want them to be rich but I'm worried that the world I've created will make them too alike - everyone is a self-serving survivalist in one way or another, and those that aren't don't last very long. "What would your character give their life for?" Well, nothing. That's the point.

Any general or specific tips for moving forward with this?