Revelations from Keynote II

[KageTokage]

I'm pleasantly surprised that they've thus far managed to avoid disclosing any information that really spoils what's going to actually happen at the end of the 4.5 MSQ. There's really only fuel for theories at this point.

The only souls we've seen posses bodies are souls with the Echo or the Resonance. Matoya, as far as we know, has neither. Body possession also seems to be linked to the Ascians and has never been shown to be something good for people to do. So until Patch 4.56 comes, I'm putting that view of the situation lower down on my list of explanations for the scene.

As far as Y'shtola talking like Matoya goes... Matoya was Y'shtola's mentor and it seems Matoya views Y'shtola as her protege at the very least, maybe even as her daughter. Y'shtola herself makes fun of herself turning into Matoya in Patch 4.4. So it's very probable that Y'shtola picked up on a lot of Matoya's mannerisms over the years. I could easily see something happening to Matoya while she tries to get the rest of the Scions back from being Called and Y'shtola deciding to take up her beloved mentor's legacy in her place.

There's been multiple instances of non-Echo related soul shenanigans in side quests, such as with Genbu and Soroban in the Four Lords quests and Lalai and Shatotto in the SB BLM quests. You could probably consider what happened with Nidhogg and Estinien a similar case.

It seems like anyone who's powerful enough and has the know-how can potentially linger after the loss of their physical body.