as someone who has a phd in sisconology, differentiating my top 3 siscons (dottore, phainon, albedo) is vital. aka my word vomit salad meal thesis
; stepcest, not proofread, contains siscons from previous works (err, drabbles) so a bit of background context is recommended but not needed, i don't repeatedly mention them being stepbsiblings bc it gets so redundant to include it every time.
to provide a bit of context, it's important to introduce the three main subjects of sisconology and a brief background information.
sisconttore: your older brother who kindly took you in and imposed the relationship of siblings upon you. he loves having governance over your decisions and autonomy as a person. he's the one who picks out the outfits you wear, the meals you eat, the hobbies you like, the ideals you adopt, and your relationship (or lack thereof) with others. his world revolves around you, so he forcibly makes yours revolve around him in turn.
siscon youngerbrothernon: an adoptive brother who was welcomed into your family after having lost his biological one in a fire. he's obedient and follows your requests without an ounce of complaint, always believing that his precious older sister is right. Seemingly harmless when observed from a base level, youngerbrothernon's degeneracy can be found in how ecstatic he becomes whenever his mean older sister insults him like there's no tomorrow, among other things...
homunculus sisconbedo: another artificial human crafted by the same creator, and by human standards, that entails you two are siblings despite looking nothing alike. he is your brother, but as homunculi, the principles and boundaries pertaining to that label don't translate over to your siblinghood. he once saw nothing wrong with proudly calling you his sister, his kin, before kissing you on the lips the second after. even after being well integrated in society, sisconbedo cannot bring himself to care about the taboo nature of your siblinghood.
after familiarizing with the subjects, the first defining question would undoubtedly be: why are they even a siscon?
phainon is a siscon because his introduction to you felt nothing like welcoming a new sibling. you dismissed him with a flick of your wrist, creating a dissonance, and didn't bother getting close until you found out he was getting bullied. his first impression of you was murky, so the admiration that followed quickly morphs into a crush. he loves your spiky personality and your honest disregard for the people around you sometimes. you mostly live for yourself, and phainon wholeheartedly agrees with that; he lives for you, too.
but there's also a soft spot in your personality. you show your care in the smallest ways, but to phainon, he feels incredibly babied and pampered in the best way possible. a simple action of leaving some leftovers for him is praised to the heavens and back when this is just the bare minimum. his sister is so loving, she's the best! :) furthermore, growing up, phainon eventually realizes the benefit that came with being your adoptive brother and learns to embrace this.
he loves being your brother; it gives him the closest proximity to you that wouldn't have been possible if he were just a, say, classmate or friend. he lives under the same roof and wakes up to your beautiful face in the living room every single day. he's like if cinderella was fucked up; he does your chores, work, and cooks your meals on a near-daily basis, sometimes coming across as your personal helper instead of a younger brother. and he likes that! :) he loves being helpful to his best and only older sister.
albedo, on the other hand, just... is. from the moment he was given sentience, the first sight he ever saw was you; the other synthetic being master rhinedottir made. it just clicks from then on, the knowledge that he will be intertwined with you regardless of your relationship. when he first learns that you are his sibling in everything but blood, he just shrugs and continues on with his life because, as a synthetic being, structures of family aren't important.
you're his sister, and then what? is this supposed to be life-altering information? he thinks not. you are both born from test tubes, marked with a star that signifies your creator who defied the rules of life in teyvat, and are routinely tasked with assignments given by her - the farthest thing on his mind is the immorality of his romantic feelings.
he wouldn't call nor recognize himself a siscon, but if someone were to point it out to him ("you want to fuck your sister or something?"), then he would just blink and agree, "yes, i do." (and he already is.) awkward time for the person who posed that question, especially if it was done in jest, only to get confirmation that the chief alchemist of mondstadt is a sisterfucker.
dottore is a siscon because he wants a multifunctional relationship with you. he longs for a family that understands his circumstance of being an outcast, but he's not content with strictly staying in the bubble of being family either. he's the one who imposed the title of 'siblings' yet he will also be the one to pop that bubble and introduce the taboo factors that will come into play. dottore can't simply just be your brother because he's bound to push the boundaries either out of personal satisfaction or from a research perspective, also because he's so incredibly greedy.
he's your brother, lover, and everything in-between. why exhaust himself looking for someone to love him when he can sate that need with the sister he had taken in? why socialize and find friends when you're here? as far as he sees it, this is an optimal solution.
he has you, and you have him. so long as this co-dependent relationship's gears keep turning, then there's no need to venture beyond the comfort and love you bring.
to conclude, phainon is a siscon because the adoptive siblings label is one that he can utilize in his favor, and he loves being babied by you. albedo is a siscon because he, an imitation of life, ironically enough, cannot comprehend why having romantic feelings for his synthetic sister is considered morally wrong. dottore is a siscon because being your brother just won't cut it for him; he wants to be your lover as well.
do they lean toward the brother side more, or does he prefer to act like your lover?
phainon ultimately leans toward the lover side more. as a younger brother, he's been treated as your sibling and just a sibling well into adulthood. you're both competent adults, yet you still treat him as that sniffling, teased boy all those years ago. he's not, but you don't seem to get the memo. at all. using his brother status is good and beneficial, proved to be useful during his late teens, but in the grand scheme of things, he doesn't want to be perceived as just that. continuously pulling the 'but i'm your younger brother :(' card only further solidified his image of being a helpless brother in your eyes.
by the time phainon realizes this, it's too late. he's always been your little housekeeper and butler, but nowadays he acts like those male mating call birds with how sensual he's been acting; he's showing off his muscles, how well he can carry so much of your luggage with just one hand, and his free hand is one you can hold onto! he's visiting your apartment without prior notice just to cook your meals, intent on showing off his boyfriend side, but all you say is, "thanks, little bro." well... at least he can snuggle into your chest under the guise of a sibling hug :(
albedo is a brother first, but it's quite inconsequential to him, actually. as previously mentioned, the line between siblings and lovers are blurred for albedo - not because of a lack of knowledge, but from a lack of care. it's translated over this aspect, too: acting more like a brother or lover? meaningless, he loves you all the same. why must his love be limited to one or the other? he can look after you, scold you for overworking yourself, and threaten to call master rhinedottir on you while also being the one who visits your bedchambers late into the night and comes out in the morning with nail indents on his back.
he takes care of you and all your needs, that's all that matters really.
dottore loves taking up the brother role so much; it's actually sickening. he's your brother, and this is non-negotiable. it'd be laughable how seriously he takes this sibling relationship (considering this is all self-imposed), if he wasn't so scary about it. as established, dottore lords over his 'big brother' title to control your autonomy, because that's what family is all about, no? you trust your big brother because he was the one who saved you from an impending life of suffering. it's only right that your trust, body, and mind are placed within his hands. he's never done you wrong because you're his precious, treasured sister.
even as a brother, dottore is already unnerving. what more when he wants to involve his mess of romantic feelings for you? the first time dottore crosses the line of siblinghood and encroaches the uncharted territory of lovers by leaning in to kiss you mid-examination, you had been greatly confused. he's your brother, he said it himself, why is he acting like this? you were naive then, foolishly believed that your happy ending had been granted by the kind man who picked you up and hauled you into his lab.
but dottore's gloved hand cupped your cheek. squished your face and told you,
"we are not like regular siblings, sister. you understand, yes?"
family endures for each other, he said it himself. so you must endure him, too.
are they bothered by what outsiders think of their relationship with you?
phainon personally doesn't care, but will begin to if it affects your public perception. he's smart and careful enough not to act like some perverted freak brother when in public with you, but on the off chance that someone catches wind of his siscon tendencies, then phainon's cheery exterior crumbles in record time. he's not above threatening that intruder to leave his big sister alone, lest he puts them through hell himself. he can go through insults hurled at him all day with no problem, not a dent to his self-esteem in any capacity. but any threat to your happiness is a serious transgression to phainon.
albedo doesn't care, and teaches you not to either. his taboo relationship with homunculus sis is reciprocal, so just like everything else in his life: public perception is bottom tier on albedo's list of worries. he'd sooner worry over timmy's pigeons before taking a mondtstadt citizen's "you're sick in the head!" insult seriously. not to say that he parades his relationship around the people, but he doesn't hide it either (ex: marjorie seeing the synthetic siblings kissing once), so some are bound to catch on. still, he tells you that it's pointless to fret over it.
there are no general outsiders to formulate a perspective on dottore's pseudocest relationship because he literally hides you away from the rest of the world. no one knows of your existence, and his own fatui grunts have no idea that he has a sister in the first place. the closest thing to outsiders would be the harbingers, who are aware that dottore has a sister (mentioned in passing), but they've never seen you before. furthermore, they are complacent because... literally, who are you for them to step in? arlecchino and sandrone will find it distasteful, but their knowledge on dottore's relationship with you barely scratches the surface level, so they refrain from overstepping the line.
furthermore, there are more than just three siscon candidates... there's 'my moon sisters are all dead so you can't leave me, too' sisconbina, 'sister, i'll save us from poverty' youngerbrothertalone, 'family is everything' sisterfuckertaglia, and 'growing up as siblings in the house of the hearth' pseudocestcchino... but that's a word salad for another time.