New theory!
Once upon a time,
Yukio explained that Rin was the child born of a union between Satan's possessed host body (now known as Goro) and Yuri Egin.
Lightning said that this happened at Section 13, the epicenter of the Blue Night.
Why was Yuri Egin at Section 13 when this occurred? Explanations have ranged from her merely passing by, to suggestions she might be a clone of Egyn. But what if she was assisting the research?
I don't mean that she was a scientist. But maybe she was doing something different? In Shura's flashback,
Yuri was constructing a doll of clay. It's reminiscent of
the description of Greenmen from volume 3.
Let's recap some information on the main character who is also connected to Greenmen. Shiemi has summoned one and has appeared with armies of Greenmen in the first anime and the Werewolf cards. She has also been joked about as not acting like a human, drifting and distant. Her visual motifs have shown her connected to the ground like a flower, most obviously in
her dream in chapter 82 and the
cover of 87.
Section 13's goal was to produce bodies for demon kings. We saw the results of their cloning experiments.
But what if they also experimented with creating different material for possession that didn't have to be a vat-grown human? This might be something that the Grigori would find palatable, since then they wouldn't have to hurt the humans they'd sworn to protect, unlike Amaimon and Lucifer who didn't care.
Time for the big jump: What if Yuri was an assistant in experiments designed to replicate human hosts using clay and flesh & blood intended for Shemihaza? And what if Shiemi was created out of those experiments? She isn't really human or demon, but animated clay. She is fragile, which is why she was sheltered in the garden and her mom was disconcerted with she got injured in Inari.
I could see this dovetailing with Takara's identity, as he is tied to a
Galatea (notice how the puppet is shown at the top of the entry). Also the text: "occasionally one might be a high-level demon, but then the doll-vessel doesn't last long". Somehow the puppet can manifest in Assiah, and I presume it's strong, maybe using it's power to keep Takara going. (Maybe some deal with the devil going on? Takara the boy born with a heart condition, and then has been bonded to the puppet so he doesn't die? I dunno, I'm spitballing.)