This is not a negative experience but the costs of the profession since I work in law enforcement and in my country prostitution is a crime and during my service I have seen a lot of shit, yes there are different cases but prostitution is not a way out of the situation.
But making LI a prostitute in a harem game is a rather controversial decision. And again, you can argue that you can refuse her but how much content in the game will be lost because of this? I think quite a lot.
I imagine the MC will gradually pull her away from that lifestyle, which she clearly doesn't enjoy. Would you not say that's a good thing?
If you're referring to why include an LI with such a backstory at all...why not? Like, life isn't flowers and roses. A flower blooming in the mud makes for a pretty good story if executed well imo, something I trust KS is more than capable of doing.
About refusing her. Mild spoiler disclaimer: If you rejected her, you gain +relations and miss out on a sex scene. To avoid this, save scum. That's it. If you accepted her proposal for sex in that specific context, you are very literally accepting that she is a mere prostitute. Now I get this is a porn game so many of us are readily horndogs, hence my save scum suggestion. But realistically irl if you actually accepted such a proposal, idk what to say to you man.
And if you are the type of person to absolutely say no to anyone who isn't a virgin, then you do you. Just miss out on her path, just as you would irl? I find it rather contradictory for people to say they don't want to miss out on Chika's path but they at the same time dislike Chika's backstory, not the way it was handled but the very basis of it. Because at that point all you're concerned about is their appearance, not their character.
That being said, to each their own. If you simply cannot tolerate it, there's always a plethora of other AVNs awaiting you.
