I agree with nomadicengi, it was probably a brain transplant. Unless Murata is going to pull some god chemical that turns adult men into high-school girls out of his ass.
Or the girl is a shapeshifter who was pretending to be a man.
Suddenly I like this manga even more. But GB is my fetish, so...
Also, after rereading chapter 10, I am pretty sure it's a brain transplant of some kind. The dude got brutally stabbed all over and pretty sure he lost his eyes. No way a plastic surgery can fix that.
Thinking about it, I bet the explanation for why she/he isn't brainwashed is because the body is female, so it got the stinger, but the brain is male so it didn't get brainwashed. So she doesn't belong to anyone.
How she wasn't affected by the sudden breaking of the car and could still use her stinger to the eye and shoot her three times.... My suspension of disbelief isn't suspended anymore, one could say, that it got twist-ed.