What are "Otherkind"?
In the broadest sense of the word, otherkind (or otherkin) are those who are not of humankind: people who appear physically to be Homo sapiens, but know or believe that their spirit/soul, mind/psyche, essential energy, and/or sometimes ancestry is wholly or partly not human. Used in this way, otherkin can mean people who experience themselves as just about anything from legendary magical beings like elves and unicorns, through known living or extinct animals like wolves and pterosaurs, to things derived from pop culture like Pokemon and webcomic characters.
The latter two categories have their own proper narrower terms, namely therianthropes (or therians) and fictionkin. There is not currently a generally agreed-on word to denote mythical otherkin as a group distinct from otherkin as a whole, at least not one with as much recognition as otherkin itself. I use mythfolk to refer to this category. Some people say mythkin, which I'm not fond of, maybe because I usually prefer to avoid the distancing implied by suffixing "-kin" to other words ("I am fae" is a stronger statement than "I am faekin"). Or one can just use both words and say mythic (or mythical) otherkin.
Otherkin can also be used in a more narrow sense that refers primarily to mythical types, mostly standing in contrast to therians. In this sense therians are not contained within otherkin; rather, the two are mostly separate, albeit they are similar in concept and can still overlap both as communities and within the same individual. This definition is less common today, except perhaps among older folk like myself who picked the word up in the late 1990s, a time when the two communities had been developing in mostly separate directions for some time and animal people were not usually using "-kin" forms like "wolfkin". (That said, it appears that in even older usage than that, such distinctions were not a matter of much concern if they were even yet thought of. See A Brief(ish) History of the Word Otherkin(d).)
Without getting too far into the weeds on a page that's just intended to provide a basic overview of what otherkind are, suffice it to say that the precise self-identifications of those who have used the word otherkin(d) to refer to themselves has varied over the decades. Mythfolk and therians have grown both apart and back together, perhaps more than once, and otherkin in general has tended to absorb smaller communities that can fit its definition, like what there was of a unicorn community some years ago.
In any case, when most people today say otherkin, they likely mean the whole sort of general nonhuman mish-mash unless they specify otherwise.
Otherkin is not...
Having a past life as X does not necessarily make someone X kind of otherkin. Reincarnation is a common origin for otherkind and the "I'm an elf soul in a human body" narrative is might even be thought clichéd by now, but it's neither necessary nor by itself sufficient. Not having an other life as, say, a dragon, does not necessarily mean one is not a dragon here and now. (Not all otherkin even believe in such things as past lives.) Conversely, having such a life doesn't necessarily mean one "is" a dragon in an ongoing sense; it could just be something one happened to have experienced at some point.
Being multiple or plural does not make one otherkin, but there is a long history of systems with one or more nonhuman members being part of the otherkin community. They often used to be called "hosts" or "otherkin hosts", especially if the members were walk-ins from elsewhere.
Being otherkind is not a human religion or a cult, although some otherkin bring forward practices from other lives or otherwise find that being nonhuman affects their approach to spirituality.
Being otherkind does not mean just having a connection to something, using its energy, or relating to it and feeling that you are similar to it. Think, for example, of human magical practitioners who identify strongly with a particular element or natural feature: they might be e.g. a "sea witch" and carry water energy, but it's not the same as being a mermaid or water elemental. Humans can also experience things like animal form shifts without it meaning they are actually a therian. (Here is a post by Sonne on how "identifying with" something is not sufficient to be otherkin, because all humans feel some connections to things that are not human.)
Being otherkind is not something you choose to do for entertainment, like roleplaying or creating a "-sona", though it is true that some otherkin use roleplaying or cosplay as a culturally sanctioned way of embodying what they really are, and some have awakened through roleplaying a character they "just made up" that turned out to have deeper origins. Whether one can transform oneself from human to nonhuman or change from one type of otherkin to another, and if so what conditions are required, are topics of recurring internal debate; but most parties agree at least that one can't just say "I'm a griffin now lol" and have it be actually true.
Being otherkind is not a gender or a way of being queer or LGBT. Many otherkin are also trans, nonbinary, gay, asexual, or whatever category you might care to name, and it's also true that some otherkin feel their gender is "caused" by being otherkin: for example, their kind may have not had any gender differentiation, or had gender concepts that don't map to the usual human ones. There are also statements of varying seriousness along the lines of "my gender is Elf"; for example, Zardoa Silverstar of the Silver Elves tells of his personal history that part of discovering he was an elf was that he found it difficult to think of himself as a "man" but neither was he a "woman".
Being otherkind does not mean you experience delusions or other mental issues. Some otherkin also have these, but the belief that one is essentially nonhuman is not just "being crazy", and most otherkin do not have delusions that they are literally, physically, 100% their otherkin form ("true form"), as is associated with clinical lycanthropy. Many of us do have occasional, frequent, or even constant perceptions related to that form ("shifts" and/or "phantom/astral/meta limbs"), and some claim non-human blood ancestry which doesn't fit in with scientific knowledge about species and DNA, but though these experiences and beliefs may be very peculiar, they are not the same as delusions.
A response to a thread on the defunct board Otherkin Community, February 2009:
"Otherkin are people who believe themselves to be something other than a human being on a spiritual, psychological, energetic and some even on a biological level, and choose to identify with that non-human fragment of themselves to the point where they count it as a permanent and ingrained part of their personal mythology and/or identity." ~ Miniar
Well said, Miniar. I too [as other responders also said] am a little iffy on the fragment/whole thing, because as you explained, I don't consider it a "side" of myself in most circumstances; it's just "me". However, it's a "fragment" in the sense that it doesn't consciously occupy every waking moment, any more than the fact that I am a hominid mammal does. Perhaps that could also be phrased as "that non-human fragment or view of themselves"?
I like that you put in "choose to identify with" as being an important point; I think a lot of, maybe even most, humans have something non-human about them, but without first perceiving this and then deciding that it is a big enough deal to merit identifying with, they are not "otherkin", IMO.
Last updated 11/12/2021