I find it funny that there was definitely a rather misguided interpretation of Sephy being this sexually experienced man cuz of his looks and demeanor Post Nibelheim based on a rather low reading of his overall character. He's more like a sexually repressed pathetic little man if I consider all the more nuance takes of him
Like if someone randomly kisses his cheek while he was not focused on them and left, he would look up at them and back down, then again, did that a few times then he just bluescreened the entire day cuz he is very slowly processing that gesture of sudden affection, not even Genesis' annoying pestering snapped him out of his trance at all
If he's ever sexually attracted to someone, he would follow them like a curious puppy trying to make sense of this allure of theirs (I think that's what your fic alludes to technically), because the man was lab grown, robbed of meaningful social interactions and lack of intimacy or even education on it until adulthood and no, Shinra did not fucking have sex ed in their curriculums for personnel anywhere, even though it's required for all ages, why would they when their great President Shinra got so many kids everywhere besides his legit one (NGL I hate that old fart but boi he made really hot sons)? That would be a funny joke
Y'know I'm not knowledgeable about the Arthur legend but in a post I read once, to explain why the knight Lancelot loved Guinevere because he was raised by some mystical lady cut off from society, he imprinted on Guinevere like some kind of sexually attracted adulterous chick to explain that he didn't know how to deal with sexual attractions
Aka the similarity is that they're both making sense of their natural sexual instincts in their inherent instinctive ways that their bodies react to, that's like perversion yes but also base carnal instincts which is not something impossible, literally everyone has that, it's just what society labels as dirty and pure that made sex such a massively messy subject
this lowkey turned me into the yapatron 3000 but...
sephy being anything but inexperienced doesn't make any sense, but i could see it go two ways (both pre-nibelheim, because post nibelheim sephy most definitely think that he's above lust) :
a) he'd be one of those people who side-eye others when they bring up sex in casual conversation, probably thinking that it's pointless and kind of stupid to allow anyone to see him this vulnerable at any given time. it's not that he's clueless or 'innocent' at all, or a matter of him 'not knowing what it is' but a genuine disinterest. even if he were to be attracted to somebody, he'd probably dismiss it as a distraction (he's not the best with feeling after all...), one he doesn't need at the moment and would probably get frustrated that he's not as untouchable as he thinks he is... which would probably make him spiral ? kinda ?
b) he's curious about it, but his overall social awkwardness (as seen on ever crisis) doesn't really allow him to go anywhere from there. i mean, sephy is a loner because he thinks he's better than everyone, i can hardly see him try to mingle or form any sort of bond for the sole purpose of sex, it'd have to be one hell of a person for him to even think of doing that (as seen with his friendships throughout the games).
but in any case, that man is a big virgin who probably has never felt even the platonic touch of a woman (or man). however, i do think that he's been brought up to be so detached from the general population and raised to be so apart from others that he does crave community (eg; the scene in the end of chapter one of ever crisis where troopers are praising him for saving them), something that he found in angeal and genesis and then proceeded to lose.
he'd most definitely love physical touch though. embarrassed that he's being reduced to an overgrown cat purring while you pet it right ? yes. that's why he'd never outright ask for it, but his partner would, of course, know him enough to know when he wants it, mostly because i picture him just... staring at his partner until they finally hug him, or give him a kiss, or drop to their knees.
uhhh... i don't know how to finish this, but yeah.