Well, I actually don't own FF7, so I'm just judging from the movie(Advent Children). In the final fight scene at the end, with Cloud, Sephiroth wields a ten-foot-long katana. I think the double blade was actually wielded by the guy who becomes Sephiroth at the end. My main point is still clear: The sword is WAY too long and heavy to be wielded by anyone except Seph himself.