The fictional character is not potentially paying the developer of the game real money. One of the big draws of these games is to at least have the illusion of choice for the player. To introduce a potential line of the story and then have it go absolutely nowhere feels disengenous to the player base.
Zanith to me seems to have, at the very least, a modicum of artistic integrity, so I definitely think the wants of the characters matter.
Now, I didn't scroll back so I might be missing some context from your conversation, but if you wanted go straight into brutal slave-fucking then the content is already there in, like, three different scenes, one of them having two branches, another four or five or something like that, and then there's the pillory scene. And if you're asserting that Lyriel should
actually become a slave for MC then you are, frankly, stunningly tone-deaf, because that has not been hinted at and does not at all fit in to the story. It's a kink that will be (and has been) catered to, and that's as far as you should read in to it.
As for the scene with a bunch of branches, that is to my recollection a Patreon-only scene so it exists solely because Zanith is
already being paid real money, so citing that as a reason to completely veer away from the established narrative is just...
eek.