They're not related by blood, however, as I said, she herself(Yuka) mentioned that there would be no incest. If it was a matter of blood, "incest" wouldn't have been particularly mentioned. It is clear the dev is going by that definition of incest(that being even step relatives).
So not by my own definition, but by the definition implied by the fact she even mentioned incest in the first place.
Also, yes the issue of your partner having had a thousand partners. Yes, that's disgusting. It would be an issue if she hadn't told you and it were never hinted at. Especially if it was only ever hinted at or mentioned after your sideways mattress scuffle. That's what I mean. No one is forcing you down her path, plenty of people in the comments have even mentioned never really interacting with her, and clearly hadn't gotten the scene where MC talks to her dad to stop being such an ass. Y'know, cus they were smart and read the cues and genuinely didn't want to get into her personal life. Maybe the town criers shoulda done that.
Her occupation was mentioned, hinted at, and vocally CONFIRMED by the time you ever got the chance to stick your dick in. And she only offered it to you in a drunken crisis, not in a romantic sober state.
If you chose to go ahead with it, that's on you man. Either way her story isn't at that stage yet. So once again, I'm not sure why people are screaming about it when she's not even an option yet.
And, y'know. They'd all be hypocrites because I know for a FACT they aren't rejecting sex every chance it comes up.
And by the way, dudes getting upset about a girl having been with multiple people(stepping away from the prostitution for a sec) is honestly funny cus it be those same dudes to have been with multiple women. Fun double standards. Although with Chika you genuinely don't know how many guys she's been with so it is understandable if you wouldn't want to be with her. That's not my issue with this. It's the harassment trying to force a label which honestly isn't even correct thinking about it logically. And even thinking about it in a "I don't want my girl to be a prostitute or OF model" if they stopped that shit before getting with you, you're not being cucked. And you weren't being cucked. It's gross, yeah. But it doesn't fit the definition.
Either way, a girl doesn't have to be fuckable/dateable in the story in order to be an interesting story addition. They coulda chose to leave her alone. Or they coulda chose to just be friends. So as I've said many times they're all still crying over self imposed issues.