Okay this is weird but I can't get this scenario out of my head......

Credence is taken under Newt's wing and falls in love with him almost instantly. He starts to think of himself as Newt's and the animals' protector given his status as an immensely powerful wizard. Eventually, once he's gathered enough confidence in taking care of Newt and the beasts, he decides that he wants to start a sexual relationship with Newt, who is very against the idea and awkwardly yet sweetly rejects him.

Given Credence's abusive past, lack of healthy social interaction and outright desperation to be close to Newt, he comes to the conclusion that he's going to try to make his way into Newt's bed, anyway, culminating in a single disastrous encounter between the two of them.

Bonuses:
-no actual rape, but Credence is forceful and scary
-Newt is a virgin
-something snaps Credence out of what he's doing at the very last second, but not before he's shoved Newt down and torn at his clothes and thoroughly frightened him
-protective yet confused beasts who don't want to hurt Credence but also won't allow him to harm Newt
-the reason Newt rejected Credence is because he is in the early stages of a relationship with someone else (Graves)
-Credence is genuinely remorseful and can't believe what he's done

Ending is up to the filler. Newt can forgive Credence and they can start to try to heal and move on, or Newt can be far too traumatized to even be around his young apprentice :(