Delicious, finally, a good question. I have a few theories, all working off the base assumption of a soul as a form of shaped energy. Personally, I think it exists within the body, during times of life. Not in any specific part, and anything that may take off part of the body doesn't take any of the soul with it. It's sort of like the thing where losing a limb makes the other ones stronger due to having the same amount of blood and nutrient intake in a body that just lost a hefty chunk of mass. Still got the same amount of soul. Obviously not something I've tested, since emotional experience is a soft science, there's the emotional trauma of losing a limb to account for, potential of undiagnosed body dysmorphia skewing results, and there's the ethics of taking someone's limb off to observe. Sadly something I don't think ever will be tested, since anyone who's throwing ethics out the window to do it is probably also ignoring all the other above issues.

Holy hell, that was a tangent. Anyway, I believe the soul is the force controlling the body. The specific shape and proclivities of each given soul isn't something I've thought much to categorize, even broadly. It's definitely a thing that can change over the course of time, as things do. One can even change it themselves, if they were so inclined. I've had a notable impact on my own, as have outside influences I've surrounded myself with. It's different than an impact on one's brain, this I know. Relating to the outside influences thing, I'd advise you all at home be very careful who and/or what you pledge your soul to. Make sure the changes you experience are ones you're comfortable experiencing. Be those changes in line with your own self-image, or what amounts to ego suicide, know what you're signing up for.