Though my knowledge of the Demonbane license is coffcoffcoff limited, I would try to answer this one.
Considering the nature of the game, reducing it to its sex scenes would be highly wrong since they’re not its focus at all (as a matter of fact, you can remove them all and get the same enjoyable game --aka the PS2 edition), although I can understand your concerns. The important matter to remember IMO is that, while all the heroes are truly kind and good-hearted, the villains aren’t. At all, ranging from selfish to pure evil.
There is one “full” rape in a bad ending (which should motivate you in not getting the bad ending; and even then, it’s foremost suggested since the event quickly fades to the bad end title), two tentative (as in “interrupted” because the victim, who is yourself in one case, is saved in time) rapes, two I don’t know whether they would qualify (one is a nightmare of sorts so I’m not sure it really counts while the other is… sacrifice to an Elder God so I’m not too sure how that qualifies either) and one I don’t really recall in which of the previous categories I should put it (that says a lot about how much it impacted me --though it happens in Leica’s route, that I liked the less so recall the less as well). To be honest, I would say that some of the rapes (or tentative) are to disgust the reader, because they’re performed by one villain in peculiar, and it’s important to feel how twisted, sick and blatantly evil he is, even more to show how not completely evil the other villains are (though they have no consideration for innocents and casualties, they don’t bask in other people’s suffering and death), so the purpose may be to make you truly hate/be disgusted by/fear said villain (and, honestly, him not trying to rape Ruri when he has a chance would be quite out of character). In other words, while rape events happen, you as the reader aren’t supposed to enjoy them but rather be outraged and want to kill the perpetrator, IMO.