Alright, let’s break this down...
There are two main points to consider here:
First — this is a porn game, and let’s be honest, a lot of people are here just for the fap, right?
Personally, when I play something like this, I’m not really into voyeurism or NTR being part of the main story. But if it’s in a gallery, as an optional scene, then I’ll watch it — because at that point, it’s just for the "fap"
Second — I need to follow a coherent storyline. The MC’s father is a powerful guy, a real tough one. He’s definitely not someone who’d get cucked. If something like that ever happened, he would kill both the MC and Rachel without hesitation.
So rest assured: there will be no NTR in this game.
Now, think about it — the only logical way to have a sex scene with Rachel would be if the MC’s father dies, right?
But if I go down that route, it could take 1 or 2 years in development for that to actually happen…
And let’s be honest, Rachel is an extremely attractive character. It would feel like a waste not to have any sexual content with her.
The only viable option, then, is voyeurism. Since there won’t be NTR, and she won’t be a love interest for the MC while the father is still alive.
But of course — if you have a better idea on how to create a scene with her, without killing off the MC’s dad and still staying away from NTR — I’m totally open to hearing it.
Okay, first of all, I don't know about everyone, but I'd say most players aren't here to fap to some text and images. If I wanted to fap, there are tons of free and paid websites with real videos and audio for every genre.
We're here for the story—sure, also for the sex scenes. If it didn't have any, it wouldn't be an AVN.
Second, sure—it's your story, and you can write it however you want. I'm not going to argue whether it's NTR or not, because that's a pointless tag.
For me, if she's a love interest (current or future) and she's getting fucked by NPCs, then I completely lose interest in her. I honestly don't care about her life or story anymore. That kind of content is for people who enjoy seeing their love interest get screwed by NPCs.
And about the scene—
I don't know if she's a future love interest or not, but if she is, it's wasted. I'm 100% sure that 90% of harem players won't follow her story and have zero interest in her sex life, especially if she's getting fucked by NPCs. So yeah, it's already wasted here.
You said she's extremely attractive, but if you really want to create a sex scene for her, there are still other ways to do it and actually attract players.
1. This was a perfect chance for netori fans—they would’ve definitely liked it, but you ruined it.
2. Make him lust after or cheat with other NPC female characters who aren't love interests, and avoid his wife.
3. Give her or the MC some kind of lust power to attract each other.
4. If you can't kill his dad, then cuck him secretly with his own women, and reveal it when the time comes.
Lastly, Just make her route avoidable or optional.
There are still other ways, but like I said, it's your story. Also, be aware that in a harem game, players aren't interested in the sex lives of NPCs.
Just sharing my thoughts—that’s all.