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This question is very difficult for me to answer. I don't have a single, simple answer to that. However, I'll just try. Sorry for my bad english, i'm not a native english speaker. I hope I'm not boring everyone to death, now.
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First of all, I have many fetishes, NTR in all its forms is just one of them. I also like vanilla, as well as Incest, to a limited extent even Trans/Futa and much more. I' am not a pure NTR fan. But I don't really care about the fetishes themselves. Rather, it is the story behind it. Yes, good stories are my real fetish. For me good stories are half the fun. For example, most vanilla or incest games often have no story at all. The plot and the characters are briefly introduced, after that it's all about getting in their panties. That was maybe cool a couple of times. But you'll soon have enough of it. Of course there are also good vanilla games, no question!
At its core, NTR itself only means stealing someone out of an intact relationship and putting them in our bed. The exception might be Netorase (Cuckold), which, depending on the design, can be both sharing and cheating. But the basic concept is quickly explained. But how NTR actually happens is always different. Because you can only tear someone out of a relationship that actually exists. This means that it must first be built up in terms of story technology. And then the reason for the NTR has to be found. That can be many things. A husband who neglects his wife; which then flees into the hands of the neighbor. A couple in financial trouble, and then a boss comes along with an immoral offer. A married woman who reunites with the love of her youth and old feelings awaken. The husband who bangs his assistant on a business trip, which his wife finds out and gets revenge on. Or you yourself as a single, who fucks everything that isn't in the trees in three. And much, much more. That's one of the fascination of NTR: it's a fetish with 100 faces.
Then for me it is also the attraction of the forbidden fruit. I am married. And of course I ask myself: what would have happened if I had chosen a different one? Lots of men have a secret crush rave on the woman's best friend, a work colleague... I think I'm compensating for my former decision to get married with this fetish, so in my imagination I'm catching up on what I've consciously decided against in my real life.
Sometimes it's just the sexual variety. I don't always want to see 100 women riding the same cock in a game. Sometimes I also find the male MC boring and another man in the game suits her much better visually.
I generally never take games personally, they're just interactive movies for me. And I'm the director. Of course, If I want to, I can consciously put myself into a role: the husband, his wife, the lover, the antagonist... I love romance, drama too. I mentally slip into the role that I like best at the moment in order to get the most out of the game for me.
As a hobby book author, atmosphere and aesthetics are also very important to me. I don't just want women to look good, I want men to look good too. Because I think they also have their claims. Render, animations, story, the sex itself, everything has to fit together harmoniously. I don't like NTR games in general just because they are NR. there are some that don't touch me in the slightest, that I even find awful. Just like in a good book, give me a pleasant feeling when playing, just touch me, captivate me. To a good book I say: "Books must have a soul". And so it is with games too.
NTR is simply the most versatile of all fetishes because, unlike vanilla, when written by the right people, NTR just really is always different. It's a fetish of 100 faces. For me, NTR's fascination begins where vanilla reaches its limits. It just covers a lot of things I love in its versatility.