The OAV replays the scene where Sephiroth is run through by a buster sword wielding Cloud. The fact he survives that means that the only thing to try next is holy water or a tactical nuke. The buster sword is almost as wide as it is long. Having something that resembles a girder more than a sword run through you and surviving probably entitles you to some claim on divinity.
Sometimes I wish I could run around with a half ton slab of metal, stabbing my enemies and anyone who watches American Idol. But there are dreams that cannot be....