I've been obsessed with negative space in game design for over a decade and I'd really love to see your ideas with the theme!
Check out some docs and previous games using negative space collision environments in game design for potential inspiration:
Inversus action game (really awesome): https://store.steampowered.com/app/432980/INVERSUS_Deluxe/
Shift puzzle-platformer game (pretty sick): https://armorgames.com/play/751/shift
My Doppelgate sokoban puzzle game (I like it): https://gunnar-clovis.itch.io/doppelgate
The Rabbit and The Owl puzzle-platformer game (not my favorite): https://store.steampowered.com/app/561260/The_Rabbit_and_The_Owl/
My Flip Stride endless runner game (like Shift but action): https://gunnar-clovis.itch.io/flip-stride
There are a few more negative space games on my profile and elsewhere, but I think this is a good base to get inspiration from. I challenge you to take this design idea and apply it to a different genre!
Also see these design posts:
http://www.squidi.net/three/entry.php?id=1
http://www.squidi.net/three/entry.php?id=2
http://www.squidi.net/three/entry.php?id=3