Had the somewhat angst somewhat hilarious idea of a mixed isekai protagonist dropped into Baldur's Gate 3 (as you do) but they're weird.
Like, not super weird, but there's shit that doesn't make sense. Not really.
They're a very muted empath even without the parasite, implied to have somehow muffled their own ability for peace of mind, initially panicked in battle but after some adjustment goes hand to hand like a fucking beast, and is very confused about all the bullshit going on in bg3. Though somehow, not surprised by things they should be. Is a bleeding heart, makes a lot of jokes, and generally doesn't seem to be taking this very seriously.
Very blaise about being threatened, giving blood, or 'feeding' Gale magic.
And everyone believes they're human, just from some weird dimension because of course the Mind Flayers were cherry picking in random places. Go figure.
Until after everyone has initially revealed their Weird Bitch Status and they just laugh.
"Ahah! Ah, man! What are the odds all of us weirdos! Not a single one of us what we initially appear to be!" And they just look at them in confusion.
"Ah, you mean your displacement in our reality, yes? I suppose it is curious, isn't it?" Astarion comments graciously.
"Ahah! No. I mean, really, none of us are human or even standard for our race when you look closer, it's actually really funny!" And they just stare.
"...you.... I mentioned it... Didn't I?"
Turns out, they're the result of a devil's bargain (playing with the idea of Harleep taking a soul in exchange for siring a 'human appearing child' or something) in a cult in an attempt to raise up a demon to take over the world or at least be prestigious enough to sire the antichrist. But the cult was raided, they were sent to live with a special family. And still deciding on the details, but they may have gotten sucked into magical girl shenanigans that ended up with them being 'purified' and able to live as a relatively normal human, not requiring sex or needing/wanting to destroy the lives of mortals.
Like, their 'sexual energy vampirism' was turned into 'I live off of the literal power of friendship' their stats are pretty damn impressive but favor heavily into charisma and wisdom.
Hilariously they have a massive blind spot to attraction aimed at themselves, often confusing it for sincere friendship, which is how they assume Astarion and themselves are fabulously good friends even if he's kind of a dick a lot. They just think they're jokes and he clearly doesn't mean it (which he doesn't, actually, since it's a performance but they missed that part entirely).
Thought it'd be real funny if they were a 'sweets' type of magical girl and maybe they get to have that power back. Or maybe it's sleep themed? Still deciding. Just either cute or cozy vibes to contrast the literal devilish intentions.
The party with Gale 'magic trick' is met with very heavy confusion when the other companions comment on them getting cozy and they run to Astarion to make sure it's obvious since they know he's the more... Sane sex expert. Almost cries finding Wyll like "oh, thank fuck you're here, everyone is being weird I think there's something in the wine..." While he's having Sad Boi hours lol
Astarion is laughing his ass off, crying, throwing up after they confess, face burning, that they have no idea how to navigate any of the actual sex stuff and it freaks them out to think about in practice or theory. He knew they had... Issues cause tadpole sharing, so he wasn't super butt hurt about it, but he does have a open offer to 'show them the ropes'.
"I think I'd throw up from anxiety and not be able to look at you for at least six months, which would be really bad in a fight so... Thanks but no thanks."
Fun news, after confession they're all very defensive about flirts towards them since they know now that there's a non zero chance they don't even fucking realize it's happening. Astarion especially is very vocally "they've got better things to do than you!" At a moment's notice, in part because of backstory but also because it's a free excuse to be an asshole.
Poor MC is confused but also gets in the habit of looking to their friends to make sure they're not missing a double entendre aimed at themselves
Harleep would NOT be fucking their kid btw, but would get real fucking suspicious and demand answers as to who TF they are, perhaps he was meant to take the kid to hell as his child after the mom died "as was his right" but the cult hid them immediately and he could be bothered, assuming the kid would die without help for their secret heritage.
A secret alt ending besides weird sex shit or killing him.