I get the feeling Natasha is the corruption route of this game.
Her route seems similar to what i saw in several games featuring corruption. Where some character tries to blackmail the protagonist into sexual acts or the protagonist is the one doing the blackmail.
She's more the pivot point.
Ashe whole sexuality resolve around the way she (well, the player) decided to react to Natasha's blackmail attempt. Starting there, routes are forced on the player; with still the possibility to not follow them at all.
I understand the need in regard of the whole story coherence, but I'm skeptical regarding the forced implications. That Ashe turn sub if she decide to submit to Natasha, okay, I have nothing to say; yet she could be switch or at least not be forced out of some routes because of that (except Lexi's one of course).
But that she become a mandatory cuck, instead of an optional one, if she let Rachel volunteer, is harder to swallow. That Rachel fall for Natasha in that route, okay, but Ashe could have just been happy for her and see this as a way to deal with the awkwardness of the feelings she have for her. Especially since herself starts to have a sex life, and then can put the feelings she had one years ago purely on her own sexual frustration.
It wouldn't really have implied more works on the game. The cuck scenes with Rachel would just be skipped on that route, and once in a while there will have been a small, "I'm happy for you", talk. So, globally it would have added just one or two hours, at most a day or two if it can't be inserted into a discussion between the two, and therefore need dedicated renders.
In the same time it wouldn't have let the player stuck with Natasha as mandatory enemy, what really feel like a forced attempt to put unnecessary tension into the story, by creating, on the
siren route and possibly on the
kitten one if the player decide to resist, an antagonist that isn't necessary; between her mind and her duplo condition, so far Ashe is already a wonderful antagonist to herself.
The worse being the fact that Natasha become a forced character on the
kitten route. Either Ashe submit to her even if the player don't like the character (either personality or model), or she have Natasha as enemy. Unlike any other characters so far, there's just no way to say "nop, that one don't interest me at all, limit her to her story part like the other characters I'm not interested in".
And to come back to your "corruption" thoughts, it's precisely the fact that she become an enemy in the
siren route that disqualify Natasha as corruption factor. She would have been one only if there were a way for her to recognize Ashe as a dome, and then slowly invite her in her own world. What would have been probably better than Ashe suddenly growing balls, and being confident after a full year of self lamentation, the instant she lost her virginity.