Disclaimer: I know almost nothing about this project and am jumping into the middle cold.
To answer the first question: So does seem sheltered and 17, though not entirely innocent; they seem to have had a rough few years.
The pacing in the interlude, which I am guessing is the past, seemed perfect. I was engaged and fully immersed, and felt like I blinked and it was over, which seemed perfect for a between chapters flashback.
"I stayed on the ground and raked my hands over my arms. It relieved that horrible, incessant itching that came when people looked at me, or talked to me, or assumed, insisted, that I was a girl, or in this case, a boy." This line almost sounds like something I would write in a journal. The emotion in and around it dug its claws in me -- a sign of fantastic writing.
Also, I'm guessing Sa* in the first part is This post has been reported for attempting to skirt the rules**er in the later section? The set up makes me think that but Sa seems a lot older than So in the chapter, though the age gaps seems much smaller in the interlude.
As for the chapter itself, I thought it started a little slow. There was a lot of detail about waking up and getting dressed. I spend too much time doing this in my books, and my cp's and betas complain about it, so I'm not sure if that is coloring my judgement of it. Either way, I think by chapter 11, the reader would or should be familiar enough with So's gender that they won't need such a detailed explanation of the binder and the logic behind it? I think that is something that should be established by now, unless the points of view alternate.
Pacing aside, the logic behind wearing the bind felt very relatable and reflected reasons why I sometimes wear one. However, that combined with the discussion of the narrator's opinions towards their breasts did hold me up getting into the story because I was comparing both to my own experiences, how I share the characters logic about binders but not about breasts, and wasn't paying attention to where the story was going. It was kind of like shouting DON'T FORGET THIS CHARACTER IS ENBY so it overpowered the scene.
The pacing picked up to a more comfortable pace once So ran into Sa. There were some world specific terms I didn't get, probably because I havent read the other chapters, but otherwise, I liked the tension.
The pacing is a little too quick in the factory scene -- I wanted to linger there in that mix of fear and confusion a moment longer, to squirm with the character, until the sounds got louder and M screamed.
The last four lines were perfect, and left me wanting to read the next chapter ASAP. I'm hoping that is what you are posting tomorrow?
One or two other comments:
"I always come back to help for tii" What is "tii" ? A typo or a world specific term I don't know?
"Unsure where to go, I scanned hanging signs as I walked, paying" This is one of those pesky phrases that distance the reader with telling. You can probably just describe what they are seeing and not say that they scanned things.
"Puget" Like the sound? Is this related to the real world, or is the story completely secondary world? I'm sure I would know this if I read from the begining.
Let me know if you have any questions.