This feels like a very elaborate plot excuse to write 2 girls kissing. Like they have to justify it through so many hoops to make it happen it's almost silly.
@monkey123 iirc Yuuri bound her breasts to appear as though she never changed in public. Considering how overwhelmingly trans she was I doubt she changed back.
Money's on Satsuki covered her in her own blood to make it look like she has a head injury to keep her indisposed. Can't die on the roof if you're passed out at a hospital.
Straight up gave yourself boobs ...
I tried constant fondling to grow mine in grade school but it didn't work. Titty skittles did wonders though.
I think protag's not telling us something.