Especially since she (correctly) anticipates that Minami is the kind of person who'd want to try switching bodies with someone just for the novelty value of the experience. Fortunately or unfortunately, they'd be far too embarrassed at the idea of swapping with each other to actually try it.
Yes, with the caveat that the number of meguca who are both sufficiently comfortable with the whole lichbomb thing to consider the idea and have enough mutual trust to actually do it is... a rather
small number.
Yeah. Anything magical follows the Soul Gem, as do any purely neurological traits because the soul is a metaphysical representation of "what a brain does", give or take. Things that influence the mind but don't originate from it (e.g., blood sugar level, physical fatigue, various hormones) stay with the body, as you'd probably expect.
Based on the information Maiko found in her grimoire, she's nearly certain that all four are shards of a single person with essentially nothing left over. She's not sure whether the original girl's body died, was left comatose, disappeared via magic, or something else, just that whatever the case may be the girl probably isn't a functional person anymore.
It won't come up in-character until you're done with the newbies (unless you specifically want to ask Maiko about it sooner, I guess?) but yeah, I'm not gonna pretend that part is still a mystery.
That said, at this point you basically won't know anything else about the girl beyond "soul magic I guess?" and "four new friends for the price of one!", plus anything you can infer by assuming that Kyoufu and Muhou loosely represent facets of her personality rather than being completely new individuals (to what extent that's true is currently unclear, and it could be a bit of both).
