Hey, ccanary01, you should probably check out the webcomic
El Goonish Shive, I think... it might give you some food for thought.
Interested? Eh... could be, Doc.
How to make this into a game? Oh, golly, there's lots of ways this could shake out:
- Fate Accelerated
- A hack of Lasers and Feelings (if you're feeling like something lighthearted and silly.)
- QAGS (another light system that has the potential for silly or serious in equal measure.
- Big Eyes, Small Mouth
- TriStat dX
- The Magpie Codex
Just to name a few.
A lot really depends on how serious or how non-serious you want to go. Is the intent of the game to have fun or to explore on a serious level how such a role reversal might make a player feel?
(I'm one of those switch hitters who might play my own or another gender or species just depending on the Feng Shui of the room or the group. No, I'm not gender-fluid IRL. It's mainly an acting challenge, I think.)
I'm not sure how freeform would work where the differences in size and strength are played up to the degree you're looking for. Doesn't mean it couldn't be done, I just can't easily see how.