I'm not sure if Klaus was that important. There was a connection between the MC and Haley way before Klaus, which didn't turn physical but IIRC both already fantasized about it.
Ultimately, Klaus wasn't important because the devs gave up on his story. But Haley makes the connection between what he did to her and subsequently clinging to her brother (when they were both much younger) explicit, and it's fairly clear that her mother isn't blind to the timing of the connection...even if she doesn't know how it manifested.
I have a deep and ongoing annoyance with most incest games because almost none of them attempt to justify flipping the attraction switch (much less following through on it) outside porn logic; there's a boy, there's a sister/mother/aunt, and they will inevitably fuck because Reasons. Far too many of them advance plots with things like sleep rape, because the authors aren't mature or sexually experienced enough to conceive of any other possible reason that a woman would want to have sex with someone who'd previously been considered off-limits. I'd find these games a lot more interesting if there were reasonable justifications in the narrative. And I'm certainly not saying that I want incest games to be tortured psychodramas about childhood trauma, the Westermarck Effect/sexual imprinting, or crushing waves of guilt that only decades of therapy can solve, because no one would play games like that.
But one of the reasons I was willing to give the Klaus story the benefit of the doubt — a wasted benefit, as it turned out — was because it could've forced Haley to examine the actual source of her obvious attraction to her brother. A
little psychodrama.
Some therapy.
Some dealing with the guilt. Not taking over the story, but an internal conflict that has to be resolved before she can move forward with their relationship. It could've taken a story and characterization that was already stupendous and made it legendary. They still could've ended up together (with or without beards), but with a much more solid foundation that we actually got.
Obviously, it ended as nothing of the sort. But it remains a wasted opportunity.