Has any actual expert conducted any kind of research on the supposed phenomenon of "multiplicity"? Has any real scientist ever even said anything about or acknowledged the supposed phenomenon? I'm surprised no one's done any research or even comments but Morgellans gets a whole research organization at my college's main campus.
Of course there aren't multiple souls in these people, especially not the souls of fictional characters created less than three years ago. What I want to know is if there's any legitimate mental illness or if these twits are just trying to get attention. I'm gonna say there's a good chance it's the latter, but I would want to see the research in to what causes such a relatively large "group hysteria" effect. What causes so many to, at least seemingly, seriously believe they have fictional characters in their heads.
Also, "headmate" seems to be a brand of toilet.
I don't think any scientific studies have been done on "headmates" or "multiple systems" as Tumblr calls it, but there IS a lot of study on actual Dissociative Identity Disorder, or "split personalities". It's extremely rare (usually diagnosed as 1% to 5% of the population), and many psychologists argue about whether or not it even exists as a specific mental illness, to say nothing of disagreements on the specifics of the disorder.
Considering the rarity of the disorder in comparison to the sheer amount of Tumblr folks who appear to have some form of it, I'm willing to bet that a lot of the Tumblr weirdos are simply fooling themselves through a sort of placebo effect: they believe that they have these "headmates", so they create personalities and thoughts and attribute them to the alternate personalities/spirits in their head/fictional characters/bullshit rather than their own brain stupidly running headfirst into a wall over and over.
Same with otherkin: they believe that they have the soul of a swan or wolf or tiger or something (conveniently almost always a "cool" or "beautiful" animal) and their brains fool themselves into having "phantom tails" that people can somehow step on or cause them to "shift" into animal behavior when it's really just their brain tricking itself and the person going along with it because they want to believe that it's true. Ever notice how they only notice someone "stepping on their phantom tail" when they can witness the person standing or sitting where they think that their tail should be?
Another good sign that it's all just a placebo effect (rather than legitimate mental illness) is that it's very easy to become a "former otherkin" or drop the idea of being a multiple system. Legitimate mental illness can't simply be "cured" and often requires continuous medication to mitigate the problem and allow the person to sustain themselves in daily life. But former otherkin/multiples tend to simply realize that the idea is dumb and forget about it.