Also, if you really wanted to use some kind of script, you could just go into the battle scene results thingy and, at the end of each battle, store the level of the character you want into a variable and, if it reaches a certain number, you turn on a game switch which triggers an auto-run common event.
But you'll have to do it yourself, lol. I can do it (I think), but I'm lazy, and it'd be good learning for you, I guess.