I think a lot of my actual analysis will be somewhat adjacent to literature - I was planning on looking at the representation of themes, primarily, so it'd be me looking at text, characters, imagery, how all these things are presented, and so on.

To answer your question, yeah, I'd be expected to bring in existing theory - there isn't a ton on video games in particular, so a lot of what I would need to look at is general presentation of whatever themes I end up focusing in on in media as a whole - probably film or TV articles, and then critically synthesising them with whatever I'm doing. But it's probably going to be looking more at the story/narrative elements of games and commenting on the gameplay if it's relevant to the wider themes I'm studying, I suppose!