Sooo, a normal move has a 6.25% chance, a critical move (psycho cut, night slash etc.) has a 12.5% chance, and plus an item would bring it to 25%. 25% seems worth it to me. Looks like the only way to reach stage 5 is to use a critical move, have a critical item, possess a critical increasing ability, and having used focus energy the turn before. Pretty awesome.