Aisha is captured by blood witches, who have found a way (a serum? spell?) to allow them to use their power on fairies. Grey is there and steps in before they get too far. But he's undercover and needs to keep the ruse going in order to rescue her... so has to keep going -- with Aisha's understanding that they just need to survive and she's willing to do whatever it takes.
Aisha x Grey + Captivity/Forced to do it (TW: dub-con)