Should "quickest rival" be taken in the literal sense? (as in, enemies with the highest Agility stat). Dark Bahamut, Dark Shiva and Penance are the only enemies with 255 Agility, while Nemesis and Fenrir are the fastest in the non-PAL version, with 200 Agility. The only ability that would fit in is Zanmato, but that's already been said.