Good pet Newt waits for master to come home and when he does he brings a new pet, a pup that lost its mama and needs Newt to mother it. Credence is meek and shy but very affectionate with some coaxing. Master makes Newt take care of the boy, nursing him and licking him clean like a good mama. But then Newts pup is to breed him! Credence often climbing up on Newt and fucking him full.

This could be consensual role play or it could be noncon with Newt already kidnapped and broken and credence added and broken. So master could be Percival, Grindelwald, or maybe Theseus?