I don't understand the NTR tag, unless this girl , that goes around braless with giant milers, have a boyfriend and the MC only talks about it and we don't see it. From his thoughts before the devil gave him the pill it seems clear he always wished to fuck this poor girl as a fucktoy with only himself feeling pleasure as a priority. After raping her in the public bath he decided to humiliate her further by moving her to the male bath, wher ehe left her on the ground, unknown if the guys decided to rape her too, probably not, but the videos are enough to crush her.
I don't understand what MC gave to the devil for the pill, maybe the possibility to return visible, usually this kind of things aren't a one sided gift
First off, it's not a devil but an angel, from the page 3 introduction he got sent down to human world for doing bad stuff and became half angel/half devil (which one he becomes depends on if he does good or bad deeds) he gave the pill to MC in hopes that granting his wish is a good deed and will get him back to heaven
Naturally, as you can see from the second last page, it most definitely did not count as a good deed