Okay okay okay..... I know that this has been going on for numurous years, and this is for now strictly rumour until it is proven in screenshots and such.
I was reading a thread posted here about being able to play as Zach even though he is dead, and I didn't believe it, because, ummm.... what was the reason? O YEAH, HE"S DEAD!! Point is that people replying to the post often mentioned the Masume ( is that spelled right? lol ) weapon that is won, and the inability to use it. That got me thinking. I was over at FF7ctiadel.com (great site), and a user reported that if you collect all 12 1/35 soldiers scattered about Junon ( or the world, I'm not sure, I only found 2, lol), and you go to Nibelheim, there is a 50% chance that a shinra guard will be walking around with a buyable key to the basement. I guess you speak to him and buy the key, then go to the basement. Sephy will pop out ( the one that died 5 years ago ) and congratulate you on collecting them, an will offer to join your party. So if this is true, then it would probably be possible to equip the sword you win on him.
Like I said, this is only a rumour, because the citadel never claimed it to be true, because there was no factual evidence. I might have this a little different than reported, so if you are interested go to the citadel and look under rumours, it will be there.
I know this is a rumour, and I'm not proving it ( yet hopefully lol ), but I thought maybe It could be one of those things square put into the game and never completed, or a really hard and complicated character to find. I also noticed when buying armor, you see the 8 or 9 charcters on the bottom, and there is 3 more open slots on the far right side. Probably just coincidence, I know, but still interesting, so I thought I'd just share it with you guys. I've only been a fan for a couple of years, seeing as I was only 6 when the game came out, so if you've already heard about this rumour , tell me that I'm full of bs, and we'll call it good, lol. that way I stop wasting time trying to get it to work.
Thanks!