Only Sephiroth can use the sword... that's why Edge could casually swipe one around with a Murasame in the other hand. That's why White and Black Mages in FF1 could use it. That's why Zidane holds two of them joined together. That's why Auron, the slowest bastard in FFX, can use it.

But in terms of FF7, Tifa tries to use it, and he just casually catches it and turns it back on her. Clearly only he truly knew what he was doing with it. It's pretty obvious really.