Starwood

powerful magician, lives somewhere deep in the woods, literally just wants to be left alone and have his peace and quiet (tm), but of course we can't have that in this house u.u
a young mirror shows up on his doorstep one day and wants to become his apprentice, but he just tells her to get lost
... she of course does not give up, being a stubborn teenager and all, and in the end he gives her one (1) chance - if she can beat his trials, she'll become his apprentice, but if she fails, she has to leave
she agrees to this and he gives her really difficult trials ... and she actually beats them
he ... can't believe what just happened, but he's a man of his word and takes her in as his apprentice
turns out she's uhhh... really chaotic, so there's a lot of explosions and magical accidents, but she got potential and also a huge thirst for knowledge
... she's also a little impatient though, that's why stuff goes wrong so dang often