Explaining My Alterhumanity
(with visuals)
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I have a slightly more concrete theory as to why my alterhumanity is the way it is, if you will all bear with me for a moment.
Let's start with the soul. This, at least in accordance with my spiritual beliefs as a Finnish Pagan, is the average human soul.

Everyone and everything has one, no matter what or who it is. However, we're going to be talking about the human soul here to explain how my (alterhuman) soul deviates from it.
The soul is split into Three Parts. The Henki, the Luonto, and the Itse.

The Henki is your lifeforce, your breath. You receive it the day you are born and lose it the day you die. To be without your Henki is to be dead.
The Luonto is your Nature, your passions and hobbies and crafts, some of your personality. A Strong Luonto means a healthy, skilled, and strong-willed person, and a Weak Luonto means an unhealthy, unskilled, and weak-willed person. The Luonto, along with reflecting in one's physical state, is often considered to be a guardian of sorts and can leave you for a time if you do not tend to it. While it is not you, it is a VERY important part of you and affects nearly every aspect of you. Importantly, Luonto are often depicted as animals.
The Itse is your Self, your identity. The Itse holds your personality, your core identity, and everything that makes up your selfhood, and is what travels to Tuonela or returns to life in a new form when one dies. The state of an Itse can ALSO affect one's physical form, as an Itse may leave or be cast from the body, which causes the health of the body to suffer immensely.
Keep in mind that the Luonto and Itse affect the physical form of a being as we continue here.
Bearing all the prior statements in our thoughts, this is how I believe MY soul looks.

I believe I have many Luonto and Itse that make up portions of my soul alongside my Henki, and that they all affect my Physical Form. I believe that due to my High Number Of Luonto And Itse, my body is Physically Inhuman, as no Human Body can remain human when has to contend with Multiple Aspects Of The Soul that have a Physical Effect. While a standard human may be able to handle having an animalistic Luonto (and even then, not all 'human' bodies can, there are so so many physical alterhumans), my body is no longer human (and may never have been) due to my soul being entirely nonhuman.
In my case, Soul affects body, body does not affect soul.

['Human' (Current Base Body), Dragon(kin), Bittern(kin), Selkie (archetrope), Enderman(kin), Nameless Ghoul (Unknown)]
Each new Itse or Luonto (I have not figured out exactly which is which just yet) that I discover physically affects my body, to the point where my very matter and makeup cannot be that of a human's, even if this body is perceived as a human to the average outside observer.
Whoever merged all of my branching Itse and Luonto together also saw fit to make it so that I could not freely change between these forms (believe me I have TRIED), or perhaps that's just an unfortunate byproduct of trying to merge so many variants on one being into a single body and a single soul.
Another byproduct of all my Itse and Luonto being in one body, is that we share a Henki. Once this body perishes, I believe all my parts will transfer together into whatever my next form happens to be.
Do I think this explanation suffices for everyone? No, absolutely not, this is just how I view myself. A strange merger of spiritual and physical alterhumanity.
TL:DR Soul's fucked up. I have a nonhuman soul which reflects physically on me and makes my body nonhuman.
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