The Tsuba Guard Kijin's specter shows Soh can divide her soul.
The created spirit uses the same model as the dark Cursed Soh.
(In the files, they are (basically)the same model)
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| Spot the difference(the little flap one is Soh's spectre. Why? Who knows) |
When the Goddess possess Yoshiro, she splits her soul and puts a piece of her inside the Maiden.
For the Ritual, the Goddess possesses a Maiden, enabling the Maiden to use her purifying power. Overtime, it caused her spirit to become cursed because of the Maiden also doubling as a katashiro. The Maiden absorbs defilement, affecting her body and eventually the spirit within. But it's only a piece of the Goddess, this is why we have Soh and Cursed Soh.
It's all because of the Goddess dividing her soul.
Cursed Soh is the Goddess. Soh is the Goddess.
Cursed Soh has the halo. Not Soh.
Yoshiro is also drawn with a halo and she has the ability to affect Cursed Soh's power. Yoshiro, too, is a vessel for the Goddess. Just like Cursed Soh is.
The vessel of the Goddess is drawn with the halo because that's where she actually resides. The Messenger is but a physical manifestation of her.
The Goddess is present in both Yoshiro and the corrupted body of the previous Maiden.
Soh is the Goddess given physical form through Yoshiro serving as an abode.
Cursed Soh is a version of Soh that materializes when the vessel is defiled/extremely impure.
But in Cursed Soh's case, she's merged with her vessel. This is why it says Cursed Soh is the Goddess who's become 'twisted with the impurities of the people' and why she has a halo.
If we consider artwork showing the Maiden physically changes upon becoming an abode, then we can assume in Cursed Soh's case, the opposite occurred: the vessel changed the spirit.
If the Normal Ending broke the cycle, we can speculate it's because:
Soh left her mask with Yoshiro, causing Cursed Soh because the two merged.
After several generations, the impurity is so potent within the 7th Maiden's body that the Goddess becomes cursed.
(I use abode=yorishiro)