I have made a post about this before, but since this thread was opened up for the Therian Guide itself I wanted to retry explaining how I believe my therianthropy exists.
This theory is more common amongst people who are Otherkin rather than Therians only because this theory provides for anything to be possible and for every type of experience to have an explanation. I don't know why exactly I began to believe that this is how I am connected to my theriotypes, but I do know that, for me, it's the best explanation for how I would explain my experiences.
For this theory, one must believe in the multiverse hypothesis, which was known to be believed in by Steven Hawkings. I will give a short explanation of this theory, but I suggest you do more research should you want to know more about it. This is a YouTube video I found that provides the best explanation about the theory:
https://www.youtube.com/watch?v=h6OoaNPSZeM
The Multiverse hypothesis is a theory where people believe that our universe is not alone. Instead of one "big bang", there were several, which all individually created their own universe with their own rules of physics. Some hereby believe that the atoms that caused the many big bangs were quite similar, which caused the outcome of their universes to look a lot alike. They are only slightly altered due to the fact that several situations happened to go down a different path than another universe (closeby).
This is where I want to mention the Nelson Mandela effect. This effect means that a certain group of people remember a certain event, look of a character, names, dates, etc, differently from what is reality. This effect got its name from the fact that many people distinctively remember that Nelson Mandela died in prison before he was ever able to get out, while in reality, Nelson Mandela died several years after doing his time. Another example of this is that a lot of people remember the Pokémon Pikachu to have a black part at the end of his tail, while in reality, it's completely yellow. Or that the Berenstein Bears are actually called the Berenstain Bears (yes, really!).
This theory indicates that somehow, one of these universes overlapped one another, causes people to cross universes with slightly altered realities.
This is where I bring in my therianthropy because this is the root of my spiritual theory of it. I also have a psychological belief, mainly with my Betta Fish theriotype which just seems to be a physical association I have with myself, but that's beside the point. I believe that everyone in this world has endless amounts of versions of themselves in another universe. Endless, so not only one's therio- or kintypes. But I think that somehow, I have a specific connection with the two universes where I am a Silver Wolf and a Betta Fish. The shifts I experience can be explained with the Nelson Mandela effect, where the two universes cross one another that causes me and my wolf or betta version to overlap in any form (depending on what type of shift).
What makes this theory so believable is the fact that it's one of the only theories that explain the fluidity that therianthropy can bring. I often see therians mentioning that they hesitate if they are kith or kin with a specific animal. This theory would explain that you are connected to a universe with a version of yourself with that specific species, but perhaps the connection just isn't as strong as an actual theriotype.
I would also explain how people can have self-invented fictotypes, or how people would experience memories of a theriotype (although this is usually associated with the past-life theory).
If you do not agree with anything I said, you can of course start a debate about it. This is simply how I see my therianthropy and how I often see other's unless they tell me they believe otherwise. I'd also love to know if any of you have the same theory or a slightly altered one!