/jp/ - Otaku Culture

Patchouli for sure. Being her apprentice comes with room and board, relative safety, and a library with all the reading material you'll need. The main hurdle is actually getting her to take on an apprentice in the first place.
I can't imagine she'd be willing to take time away from her personal study to put in the years required to turn a baseline human into a magician for nothing, but I'm not sure what I would be able to offer her when she already has familiars and mansion staff to do basic chores and run errands. Promising to be her underling after becoming a magician is more or less all I can think of, but I don't think she would find a magician underling very useful when she can probably send Sakuya to gather ingredients or buy relevant materials anyways.