I do not understand why people are so against NTR. Besides D, the MC has had his way with Elena, Jennifer, Georgina, Olivia and Margo. This isn't a harem game. Why can't D get a little non lesbian side action if she wants to?
By the simple fact as it is written D.
The game begins with an innocent, naive, shy girl, ashamed of her own body, who ends up falling hopelessly in love with her father who shows her how much he loves her and that he always loves her will protect.
Do you really think that a person who has these feelings for someone could even look at others? For me, corrupting D is fine, but not in the NTR sense, there are more ways to corrupt her without totally incongruously destroying the girl's BG.
I do not mind the NTR if it is well built, but trying to pass an NTR for "corruption" in a girl who is totally the opposite of someone who could easily cheat on her partner, makes her lose a LOT for me.
A clear example of a well-made NTR is for example "summer with mia" (spoiler of the game, watch out) where although you let Mia seduce her father, at the moment where she was supposed to fuck with him, she just didn't she can because of being in love with the MC, and in this game (in SwM), Mia is not as innocent or naive as D, however Incent Games did very well in giving coherence to acts and thoughts and development from the girl herself.
Of course, this is only my honest opinion and how I understand the game, Im not trying to say Im absolute truth or something like that.