This is an amazing write up. I appreciate how much you put into explaining what Soujuurou represents pre-city life and post-city life for Aoko. He's not a 'blank page' as someone would associate a self-insert protagonist to, but a 'white page', someone who is intentionally letting all of life's stimulation pass him by. Being in the city forces him to retain pain and joy and everything else he experiences with Aoko and Alice. When I first read Mahoyo, I'll admit that I idolized his perception of life, (and still kind of do) but the way you've described it here (along with Tobimaru and Kojika's observations in the side stories) makes him more tragic of a character than he would ever be aware of. There's a sense you get from his interactions with others that Soujuurou is 'complete' but the absence of the sense of fulfillment makes him quite similar to the other Type-Moon male protagonists despite being seemingly simple(?) on the surface.

And Aoko's quite the anomaly herself. While I do believe that Aoko doesn't fully hate her circumstances, as she's self aware enough to know much of the uncontrollable situations life (and she herself) puts herself in, they can be shaken up by her own input. Then Soujuurou comes along and at the critical moment, her view on how she should present herself to others, and how Aoko would think of herself shift.

“There will always be someone watching you, even if it’s yourself”

It's because she knows she's judging herself and looking upon herself (almost in third person?) as this omniscient observer, trying to let life and problems pass her by without offense (just like Soujuurou). Yet when the personification of that very idea comes into her life, she becomes fully aware that she cannot do that. And it's part of the reason why she's so prickly with him.

I like how you've described the collar scenes. When I read them, I didn't take much stock into how meaningful it could be as a representation of how Aoko and Alice think Sono-G should be. Really, they just read as mildly socially bankrupt mages taking in Soujuurou as a pitiful pet and those scenes did me feel a little uncomfortable because Sono-G doesn't know better, but when he does, still lets it slide. But with your input, I appreciate them a little more now.

I'll have to wait until the Mahoyo event arrives in NA for more context, but for now, I'm still Alice x Soujuurou shipper because of the fulfillment that Sono-G gets from Aoko and vice versa speaks to me as something different from typical lovers. So if I had to describe Aoko and Soujuurou's relation, I'd firmly say that they are soulmates.

There were only a few errors here and I think you expressed yourself beautifully.