So I've been rereading this series yet again and noticed that Yuuyake is present in the flashback where Shinozaki becomes a human repository. Yuuyake has also said that she has not used magic in around 15 years, which seems to line up with approximately that time. I suspect she knows what Shinozaki is wondering, but has never seen fit to tell him, perhaps due to shame or regret? A magical accident perhaps?
I'm still wondering what connects him with Mahiro. We only have brief snippets of her here and there, but their personalities don't seem to align much, nor does he appear to have a similar world view or philosophy (at least, judging by the newspaper article flashback story).
Huh. I know there are only a few more chapters now and I've seen the TL notes saying that (some or all of?) this stuff is explained eventually, but I wanted to get these thoughts out. Also, gigantic Fuyugare watching them in the last page was kinda weird.
Edit: Oh. I see. Yuuyake made the barrier, and Hazakura suspects that the barrier she repaired and the human repository magic were both done by the same person—i.e. Yuuyake was the one who actually turned Shinozaki into a human repository? That tracks more personality-wise and fits with the magic history, but not Yuuyake's non-existent magic competency. The whole spiel about desire and channeling energy through the conduit of one's ego would make sense, however, as child Yuuyake seemed to have an entirely different personality. But Yuuyake didn't actually confirm Hazakura's suspicion...
Was it young Yuuyake's dream to create a cyborg, in the same way that Shinozaki was briefly excited by the prospect of being one? That would be cute, but disappointing if that were their connection.