Graves needs information Grindelwald has. If he doesn't get the info, people will die. He knows it's a long shot, but he goes to visit Grindelwald in prison, offering certain luxuries if Grindelwald tells MACUSA what they need to know. Grindelwald rejects Graves' offers, but says he'll tell Graves what he wants to know if Graves begs Grindelwald to fuck him. Graves agrees, only when he does it, Grindelwald tells him he's not being convincing and makes Graves try again and again until Grindelwald is satisfied that Graves 'means it'. Only then does Grindelwald hold up to his end of the bargain.

It's up to the filler whether or not Grindelwald actually fuck Graves or just makes him beg.


Bonus if Picquery knows about the deal, doesn't force Graves to make it, but doesn't try to dissuade him either.