@Seblak only reason it is even remotely coming off like that is because the adaptation sucks ass when it comes to the MCs personality and interactions with others.
in the novel (iirc, was a bunch of chapters ago) the saintess liked him from the getgo, and was on board with the price tag thing, since they flirted with one another and she knew how the event world works and what she essentially was. Also the people he took over with the dark energy only did a little prodding here and there, no mental brainwashing magic needed. Pretty much everything between the two of them was consensual.
Now what wasn't exactly consensual (as in neither of them had any idea whatsoever this would happen) is how she gets to travel with him from here on out throughout the story that will either be in the next chapter or the one after. depending on how much the author wants to rush this.