User blog comment:IamJakuhoRaikoben/Chapter 285: MPF, Review./@comment-16344653-20120602180659/@comment-5782519-20120603040408

All of it was Cana's power, all Mavis did was "grant permission" (so to speak) to use the spell.

In other words, seeing Cana run out of magical power is almost impossible right now.