I can see where you're coming from. I'd agree - if that was the situation.
But sex wasn't Syphii's only choice - she willingly agreed to it because she also got benefit from it.
Here's why:
Syphii and Vagrah are spirits who feed on ambient energy. Drawn by such energy, she wandered into Vagrah's territory. A battle ensued, one she lost. Normally, spirits would just kill each other, consume each other and go on about their business. But Vagrah offered her a choice, die (which is the normal result of a lost battle) or stick around and get what she initially wanted - by entering an agreement for sex. In addition to this, Syphii also had the choice of leaving altogether.
She decided it would be better to put up with his demands - and in return she would get to absorb the energies there. This doesn't quite fit the description of what you've mentioned here:
It actually makes their relationship mutually beneficial.
In addition to those reasons, Syphii was generally free to go wherever she pleased, do whatever she wanted (which is how she even meets the main character) - provided she slept with Vagrah every few days as per the terms of their contract.
During this time the guy didn't even worry about or bother her.
Does that actually sound like someone who's being forced into a sexual situation? I think most people would agree it's a begrudging sugar daddy / sugar momma situation at the least.
The last point I'd make is this - I haven't changed or altered the scenes in any way since I made them. Furthermore all of this is explained in detail - directly from Syphii's mouth upon meeting the main character.