i would say that this character would have to be a fella (I'M JUST FEELING THAT OKAY okay), and one with thick skin, because he would be abandoned on a regular basis due to the fact that john and isaac have a problem called Flirting Endlessly (what else is new). this character would most likely be an investigative journalist for john's newspaper, gifted with psychometry, so they can pick up brief visions from inanimate objects because JOHN LIKES GIVING OUT NOSY POWERS. he would also need thick skin because john for one will love to be insufferable towards said apprentice (which may get worse over time given his growing attachment to isaac and resentment that one day said apprentice would have to take over his job) so ... yeah again GOOD LUCK