"I can effecitvely wield six at a time," Zack offered, smiling faintly. "Which is... a lot. And some people link their slots together, but I don't need to do that to get the effects of different materia to play nicely."

A pause, and then he explained, "It isn't something everyone can do, but I can actually take two materia and merge them to make an entirely new one. Which is useful when you've been out adventuring and you have a million blizzards or something."