What would say if I told you that my pure self likes a VN about raising a slave?
Let me explain my rationale.

I have found that, in stories, one of the things I like most is "helping/curing" characters in whatever way possible, and that that help distinctly affects the person in question.
This directly translates to my favourite types of heroines: Kuuderes and Tsunderes. Haruka in Never7 is a girl who is not particularly good at communicating, but the entirety of her route is spent on fixing that, with a good dose of love involved. To this day, that route is still one of my favourites. Tsugumi in Ever17 is yet another example of a character who slowly learnt to trust, through the power of hard work, abusing others, and love. That makes for another favourite character. And the pattern repeats for most of these archetypes. It's not a matter of "cool beauties" or some such nonsense, it's a matter of helping them and curing them of their problems.

"Curing" isn't the only factor. "Causing change" is a pretty big factor in and of itself, an characters with great character development as a result of love always spark my interest. Most of the time, said 'development' ends up being an increase in happiness, which leads to some pretty dodgy 'development' that can basically be classified as turning the girl into a nymphomaniac.
And its when you get to this extreme that some of the 'darker', more problematic sides of my preferences come out. When what I'm looking for is the process of "curing" a character, there's nothing that necessarily forbids breaking said character in the first place. And indeed, in some stories I've read the 'plot' involved getting the characters addicted to sex, and then learning moderation, which is a twisted way of interpreting the whole thing, but very much within my strike zone. First there's a heavy "change", and then some "healing".

This leads to my fondness for games like Rance and Bunny Black. For the most part, Rance's objectives lie in increasing women's favour, leading to him helping them, and eventually having them fall in love with him. Otherwise, he can also cause a problem for the girl, and then fix it, or even force himself upon the person until they learn to love him. All means to an end, and a rather pleasing end -- making the woman happy, helping her in the process. Whilst there are many examples to call forth in the Rance series, the first one to come to mind is the sex slave you can get in Kichkuou Rance. There, you get the option to rehabilitate her. And the whole process is a painful/happy experience, with her finally attaining happiness at the end. But Rance can also leave me hanging, such as Elizabeth at the end of Rance VI. Bunny Black works the same way, with a gentlemany-ish protagonist who may force himself upon women, but causes deep change within them. Even if it is turning them into nymphomaniacs... The idea is very clearly depicted in the character events. Initially they show a terrible hatred, which turns into dislike and slowly blossoms into love. Not in a pure way, most of the time (they just want sex), but it's something. Some of them fall in love with the "gentleness", which is a ridiculous notion as we're talking about rape here, but those are also some of the purest feelings.

Which is why one of my favourite stories is definitely one about taking care of a slave who was previously badly treated. This gives one the opportunity to "rehabilitate" the person, teaching them that they're allowed to sleep on a bed, to wear good clothing, to eat a decent meal, to express themselves, to love. The character, then, undergoes deep change and growth, and it's all for the 'good'. There's also the option of causing change through sex, if you'd prefer that way. The same developer also made a VN about a bullied girl, who you treat well and 'rehabilitate/fix her life', which basically plays with the same ideas.
It certainly is twisted that one would abuse (not in a physical sense) a person with mental scars to manipulate their emotions into liking us, who is helping her, but this fits nicely within my likes, and it's also good for the person, and also causes them to be happier. All's well that ends well, I say.

If you want to bring my tastes to a better light, then you have Kamidori. Kamidori is, in many ways, a story about changing for the better. It is the story of a young alchemist who, through his hard work, attempts to make his city a better place and attempts to help all around him, including the 'monsters' and 'unknown beings', changing all of them, both humans and other races, so that they learn to live with one another. By helping these many races he lands, of course, all the cute girls, but that's only a side bonus.

So then, do you know of any stories/VNs with these characteristics? I take on everything. For instance, the other day I was considering one of those dungeon games where the protagonist gets raped by monsters, except apparently the monsters really started to like him and end up following him.