"Well I hope it's hard for you to, I dunno, set things on fire in a biology class. But other things'll happen." Because this is Fai, and if weird things don't happen, Toushirou won't know what the hell is going on anymore. It's not even a dig at Fai's intellect, because he knows better. You get Fai to focus, and he has a perfectly serviceable brain. But he's strange, and he's supposed to be that way. That had better be the same.

"Nah, that much comes easy." But it'll be after a while, because he has to make sure he's in proper shape. That his powers are working right, that he still knows how to handle himself in a fight. And get used to the idea that it won't be the same idiots he's ordering around.

That last bit is big, but he won't say so.