below the cut, you will find my personal belief about doppelgangers,
along with how it applies to kathe and adriane.
this is very long so be prepared to read. ( some parts may seem like babbling, i'm sorry. )
@polycephebi
much of my beliefs on doppelgangers come from irish folklore and paganism, particularly the irish fetch. a smaller portion of my beliefs stem from the concept that doppelgangers are two halves of a whole. i would've included some japanese folklore for kathe and dri, but the ikiryou do not fit the nature of their relationship.
admittedly, much of what we know of the irish beliefs of the afterlife and souls is lost. and what we do know, of the irish and others under the umbrella of the celts, was written by the greeks and romans. thus, much information out there are those that have greco-roman influence. ( keep in mind that the celts were extremely widespread. my beliefs come from that of the gaels, which is the combined areas of ireland and scotland. celtic language and culture of the gaels originated from the irish.)
carrying on ! i and some other irish pagans believe that souls experience a cycle, similar to that of reincarnation. the soul does not die, but returns to the otherworld, which acts as a place for souls to rest and reflect before they return this realm and become a human once more.
with the belief that doppelgangers are two halves of a whole soul, and the folklore of the fetch, a particular concept formed in my mind for kathe and adriane.
130 years ago, adriane came into existence. and 98 years later, kathe was born. then at the age of 111 and 19, they met. looking nearly identical, with their eyes and voices being the only noticeable differences. but years before that, when kathe was only a child, adriane had used her as a host for several years. i have always had a belief, if not entirely canon, that when taking her as a host, his soul pushed out kathe's original soul from her body.
her soul tries to get back into her body. of course it would. those moments of her soul trying to squeeze back into her body would've only felt like tiny slips of control on adriane's part. when he finally left her body, instead of leaving a space for kathe's soul to return to, there was something still there : an incomplete version of adriane's soul. almost as if a fetch had tried to form, only to be stuck inside of kathe. it's not to say that there wasn't any room for her, but something was still there, keeping her from solely occupying her body once more.
it could be compared to kintsugi, where his partially formed fetch filled the cracks of her broken soul. ( no, i am not comparing him to gold. ) he became a part of her, the glue that kept her soul from staying broken and fragmented. kathe became connected to adriane without either of them knowing until they had met years later and felt the pull. a connection neither could explain because she couldn't remember and he would have to take some time before remembering what he had did all those years ago.
this isn't to say that adriane was free of kathe's soul when he stopped using her as a host. a piece of her soul stayed connected to him, a piece that had wiggled into his soul, too small to be noticed.
kathe wasn't originally going to grow up to look like adriane. she would've grown to look like one of her aunts due to dominant genes from her father. but having a piece of adriane's soul changed that. it's another element of them being connected. because of him having the more 'dominant' soul, he influenced her more than she influenced him.
being around him acts as a missing piece for her equilibrium. she can function as her own person just fine, but the connection she has with him is the tiny piece that she didn't even realize she was missing. she feels more stable around him, more understood. he's the best at grounding her because he has a piece of her that gives him that same pull. the same tiny, missing piece to equilibrium that he can function without, but feels whole when it's there.
it makes adriane both the worst and best thing to ever come into kathe's life. worst because he was a catalyst for so much hardship, but the best because when they met again, he let her in ( albeit in a less than healthy way ). she treasures him because she subconsciously feels complete in the sense of self.
kathe's current appearance is nowhere near the doppelganger she once was to him. one would think that this is a sense of growth into her own person, but it's not. it's a regression. nearly a decade without her soul being complete created something else, something that while still her, is not her truly.
the long hair, the soft clothes, the feminine choices ; they're all a step backwards. some of her weaker traits have come to the spotlight without adriane's presence. it's not to say that these traits are bad, but they were never this prominent before.
for her, growth would be marked by returning to her status as his doppelganger. it's her regaining her equilibrium. the day she cuts her hair and puts on her tomboyish clothes will be a good day.