May Sei sense magic on your character? How much do you want him able to tell? He has no soul. It's kind of obvious. He's used to people noticing.
May he use this information to be a jerk to your character? Wow why would you be an ass to him how rude. sadpuppyface.
May Sei's singing voice have a soothing effect on your character? How much? tbh a good singer doesn't need magic to get Dorian under their sway you're fine