So Credence gets a wand and is just learning how to use magic, when a spell goes wrong and he ends up with a self lubricating ass thats leaking at all times. He goes to Graves for help, but ends up being too shy to ask him about it. However, Graves can smell it on him, and takes full advantage, not being able to control himself and fucking Credence for the first time. It can end with either Graves helping him reverse the spell, or Graves knowing how to reverse it but keeping the knowledge from Credence, because its just too damn good for him.