i suggest using the final attack +phoenix, but that's more for the emerald weapon, but to beat a weapon you just need to level up and play it by it's rules, emerald says not much materia (air tai force deals 1111 for every materia you have equipped), ruby says 1 on 1 fight, so level your best guy up and hope for the best and try different styles. such as counter+mime and use a combo before that such as hero drink and elixir, if you need some more elixirs, you can always use the W item glitch if you don't have many on your person.
(you get mime from one of the 4 sacred materia caves, just breed some chocobos or use a editor to warp to the materia cave's location if you do not wish to breed chocobos)