Watashitachi wa Moto Joshi desu - Vol. 1 Ch. 7

[Litreara]

I hope your right but I personally think the scares were from physical abuse.

Spoiler

When I made this comment, I assumed the manga wouldn't focus on real-world science, leaving room for a different 'treatment' approach, especially given the overnight genderswap. However, since the 'treatment' for the genderswap is entirely rooted in real-world science, it’s likely to just physical abuse—possibly cigarette burn marks.

 

[Bourbon]

Hm wonder why Nagisa think like that.


Also wtf happened to his back?

I'm just reading this for the first time now, so if I'm right it's 100% a guess, but it seems pretty clearly set up that Yuuki's dad abused the shit out of him when he was a girl, putting cigarette butts out on his shoulders and taking a belt to his lower back, and that he was able to finally turn the tables and defend himself from his father after becoming a man with the strength that entails. The appreciation for that strength is why he's now an athlete, and why he can't understand why Mino would want to go back to being a "defenseless" girl who can be easily abused. The latter was set up last chapter, with Mino already being much stronger.