People keep mentioning the game "our fate". Never played it but I saw people talking good about it.
Our Fate is a realistic story about a father meeting his 18 year old daughter while not knowing she even existed before. Our Fate had four main paths: "good father" (not getting romantically involved with her), "romance", "cynical" (MC acts tough but is not a bad guy), "hard corruption" (evil). The first two paths being "light" and the last two "dark". So, dark is more from the perspective of the daughter than from the MC, but it is describing the overall tone of the story (in those paths).
Sadly, Our Fate has been abandoned / on hold for years now. The devs of "Lost at Birth" wanted to make a continuation of "Our Fate" but the dev of "Our Fate" broke radio silence and forbade them to do that.
It is my understanding that Lost at Birth will not be a remake of Our Fate, but will follow more or less the same premise and paths.
Even though Our Fate seems abandoned for good, I still recommend playing it. There is plenty of content, although no
sex with the daughter unfortunately.
And a good story with a Harem is even more harder.
I think realistic depictions of harem are extremely difficult for a good reason. Incest is already something unusual IRL, as is harem. Combining these two makes it exponentially harder. Especially since you need to spend a lot of time to build up both types relationships, as well as the interaction between the (prospective) harem members. Most games fail on all of these accounts but especially the last one seems very difficult.
You may want to check out Petal among Thorns and Midlife Crisis.