Rapid fire Serana headcanons it is!! Mine is significantly different from how she is portrayed in the game, so this is gonna be fun!
One thing I've always felt with Serana is that her backstory and her dialogue were misaligned, like they were written by different people. Unfortunately, I have more than passing familiarity with the kind of family situation she grew up in, I pulled on some of my own experiences to try and tweak her personality to be what I felt was more natural for someone of her background.
The first thing is politeness. Serana to me is someone who knows how to talk, not to socialize - she speaks in a formal register with few contractions and with somewhat antiquated vocabulary. She rarely shows her emotions outwardly, and practically never curses in casual speech or even in her thoughts, with something even to the tune of "damn" or "blazes" being harsh speech to her ear.
(I also imagine she speaks with a more posh accent, closer to Laura Bailey's work as Vex'ahlia rather than her unmodified Serana voice)
Another thing I tuned is her sass/sarcasm. The underlying tendencies are still there, but given her isolated environment and complete lack of true peers, let alone genuine friends, means it never became as much of a habit. The way I usually describe it is that game Serana feels like a midpoint than her starting point in my fic - there's a lot of mental barriers she has to work through before she reaches that level of comfort with expressing herself, and part of that development is finding a social circle that accepts her for who she is and allows that personality to nurture and develop.
Another thing where my writing disagrees with the game is Serana's value systems, because despite the common perception of her in the fandom, the actual writing faffs about the subject a lot in order to accommodate both the good and evil routes for the player. This results in a somewhat dissonant characterization around certain topics, for example the subject of Molag Bal, where Serana will openly lament the results of her family's worship of him and consider the ritual degrading and traumatizing, yet will also praise the player for open mindedness should they say they worship Molag Bal too.
In my fic, Serana has a much more hardline stance on this. She is, despite her circumstances, a kind person - but one who has had to shell that kindness under a lot of masks to preserve her mental and physical health in an environment that punishes it. She tends to assume the best in people, sometimes to a naive degree, which contrasts with Saya's cynical and pragmatic behavior.
She has had a long time to reckon with how she feels about Molag Bal and her family, and at the crux of troubles is the internal dilemma between the objective atrocities that Molag Bal has asked of (and inflicted upon) them all, and her instinctive need to justify or rationalize these actions to herself because of the love - however misplaced it may be - she feels for her mother and father.
She has the awareness to realize that what she and her parents have been doing is wrong, not just because of the harm it brings to themselves but also to others, but it's a much longer road towards unpacking all of those things one by one and coming to terms with the resentment she feels towards herself and her parents because of them.
In my fic, Serana is someone who is deeply, deeply curious about the world. Her isolation on her parents' island has left her starved for new information and experiences, and an outlet for much of that has been books - leaving her with a somewhat skewed, almost idealized perception of reality. Her knowledge is at once deep but very patchwork, with odd spots of encyclopedic insight in specific topics combined with complete ignorance of the more mundane aspects of the world.
For lack of a better word, Serana lacks the apathy/disinterest her game counterpart holds towards everything outside of her immediate circle. She is curious about people, she wants to see places, she wants to try things - but at the same time it's all incredibly overwhelming just owing to the sheer amount of unknowns. She's not blind to being lied to but she's rather easily taken advantage of, in part because she generally assumes people's intentions to be clearer than they really are.
Also, she holds a kind of... revulsion, so to speak, when it comes to the subject of violence and killing.
Serana is absolutely not a stranger to inflicting physical harm upon people, but context matters: she has rarely, if ever, done that in a situation where her life is actually in danger. Feeding always happens with pacified thralls. Her mother's lab studies always happened in controlled conditions. Combat always happened in context of training. Much in the same way that people who eat meat regularly are not necessarily capable of killing an animal - Serana's ability and need to feed on people does not necessarily translate into her capacity for inflicting harm to others.
It takes effort to "mask up" and detach herself from the act unless her life is literally in danger. The fact that Saya can do that at the drop of a hat - and takes lives not just for survival but even simply for money - is something she takes a good deal of silent discomfort with.
I have mentioned this occasionally in my previous posts, but Serana is both autistic and demiromantic/demisexual in my fic, which colors almost all of her social interactions with strangers and friends alike.
Serana is at once very good and very bad at reading people. She's observant: in her inner monologue, she's constantly studying people's language, their expressions and body movements, essentially trying to squeeze out as much information as she can to respond appropriately to any given situation. It helps that she has also been tutored extensively on this very subject for the purpose of courtly behavior.
In essence, Serana views every interaction as a call-and-response. Every interaction is a series of branching decisions, each reaction is mentally or literally rehearsed ahead of time, nothing is ever completely impromptu with her - which is why being ripped out of her comfort zone in the castle has been profoundly distressing and disorienting to her. She's very unused to being allowed to speak freely, and the fact that Saya insists that she does is a big part of her developing the agency that she's been denied for most of her life.
Similarly, most forms of attraction are functionally foreign to her, as she has never grown close enough to anybody to actually experience and dissect those feelings (until Saya, and even then way down the line). She understands notionally that she is attractive, and can at times make use of it to get her way, but she also does not really understand what it's like to be attracted in such a way, or that her attractiveness is not something she can just "turn off", and is broadly ignorant to the effect her presence has on people.
5. Vampirism and trauma (TW: CSA discussion)
Serana's feelings on vampirism and her parents alike are complicated, and broadly modeled on the phrase "illness protects itself".
As I'd mentioned before, she broadly understands vampirism to be a negative due to the effects it has had on her family - but what she does not fully internalize yet is that vampirism itself was an effect, not a cause, and that her family was already very dysfunctional to get to that point in the first place.
Valerica and Harkon were an arranged marriage between a lord's daughter and a minor noble, wherein Valerica's father owed Harkon a debt he could not settle except by functionally selling off his own daughter to Harkon. Theirs was a loveless union. Much abuse was involved, of all kinds and varieties, and in the fic it is implied that Serana was an unwanted child born of one such "encounter" between them. Once Serana herself grew up and Valerica became less malleable, Harkon switched his attention to her and Serana herself was subjected to routine psychological, physical, and sexual abuse.
Molag Bal was not her first experience. There is a reason why her danger response is freezing first and fawning second.
Due to all of this, Serana feels extremely conflicted about her vampirism. On the one hand, she despises it - it is a stain upon her mind, body, and soul, a material and irrefutable proof of her being damaged, of the abuses she has suffered and continues to inflict on others to sustain her own selfish existence. On the other hand, she clings to it - because it is proof that she has survived, that she endured, and that she has become stronger for it, even if it is a power she loathes to use.
She fears it. But more than that, she also fears letting go of it - because doing that would mean admitting to herself that none of her suffering ever held any meaning and that none of it had to happen. And that's not something she can accept just yet.
And now, a collection of rapid-fire characterization tidbits, in no particular order:
Serana is a polyglot, fluent in post-Atmoran dialects of Old Nordic, classical Aldmeris (which is mutually intelligible with Altmeris), and knowing a somewhat archaic form of Nordic Sign Language.
Her birthday is the 11th of Morning Star, which means she is a Ritual sign. She was born during the Middle Dawn, and does not know her exact birth date or age.
She was 22 years old when she became a vampire. This number is meaningful.
She was sealed away on the 29th of Sun's Height, 2E523, almost exactly 1008 years prior to her release. This is also the same year that my Vestige was born.
She is an extremely competent alchemist and, although she dislikes talking about it, an experienced surgeon.
She dislikes rainy weather, and autumn is her least favorite season because of it.
She has never seen most common Skyrim animals in real life. The two dogs in Volkihar Castle are actually Harkon's, and they also used to own a cat until one of the hounds ate it.
She does not know how to use any weapons, and her "dagger" is actually just an overly fancy letter opener.
Vampirism enhances all her physical senses, which combined with her autism means she frequently finds herself overstimulated in bright or noisy places.
Her favorite color is blue, with no preference toward particular shades. However, she thinks red suits her better due to her pale complexion.
In combat, she is first and foremost a cryomancer with a lean on supporting fire. She does not use lightning magic like she does in the game, but she does know it.
Similarly, while she is a very skilled conjurer and necromancer, she prefers not to employ that skill unless absolutely necessary, and would rather summon atronachs if the situation requires.
Her eyes used to be naturally blue. However, vampirism has turned them a dull brown which shines red whenever she uses blood magic.
She is a capable illusionist and frequently uses glamour to tweak her appearance in small ways and conceal her vampirism from those with an eye for it.
She has an interest in astronomy, and used to go stargazing with her mother when she was younger.
Animal motif-wise, her bird is the magpie due to its association with intelligence, shinies, and omens :)
Ever since her awakening at Dimhollow, she has suffered from partial amnesia that makes it difficult for her to remember her early life in much detail. She has not mentioned it to anyone, and the cause has nothing to do with her imprisonment.
