Tamara manipulating the MC into unknowingly fucking her with voodoo magic and Tamara fucking MC are most definitely not wildly different points on the scale. I'm pretty sure there's only one way that train goes from that point. She wanted it, MC wanted it, the perfect situation popped up and they both got what they wanted.
Quick progression of Tamara events. She masturbated while MC was snuggle up with her playing with her tits. She sucks MC's cock. She has her mind absolutely melted with repeat orgasms by the MC during a torture scene. She manipulates him into voodoo sex. They'd already done pretty much everything else there is to do and were at peak sexual tension. Throw in some mind altering incubus magic and they were gonna fuck, her walking in on the MC already in the middle of sex cemented it happening right then and there.
I swear I've never seen so many people playing an incubus sex game complaining that the sex is too sudden. Where tf do you people actually come from?
