lol this is a funny story. i played ff5 with my cousin and it took us over a year to beat it since we both had to be around to play and also the game got boring at times so we stopped for months at a time. we split up the characters so i controlled 2 and he controlled 2 and we could do w/e we wanted with them without question. (except items and equipment we would work out who gets what) anyway i forgot the levels but when we got up to that boss we had only 2 coral rings. (i controlled the main character and faris) to be honest his characters completely sucked. he would just choice abilities randomly and master ed stuff he never used so i made 1 of my characters a primary fighter and the other a master is all magic classes. (not literally mastered...just enough so they could cast all spells even if they were listed as secondary magic) heres what we did:

gave both coral rings to me cuz his characters were better off dead anyway (i just told him to be a thief and try jumping right away lolz i forgot if it worked =/ doubt it tho) for this fight i had my fighter as a samurai with Sshot so i could attack 8 times in a row (sorry but i forgot if the samurai held 2 swords...if not a samurai i was a ninja with samurai weapons and if not that then i prolly went bare mixed up the 3 abilities so i could do this). i just used Sshot as fast as i could each time his turn was up. my other character was red/time so i could cast twice...(i dont think i used haste2 for this fight but u can try it) i forgot the spells name but it transfers the mages turn to another character) i used that twice...once on my warrior then back onto my mage this way by the time sshot is done im ready to do it again and my mage doesnt have to wait too. (this only worked like 3-4 rounds then for some reason it just doesnt work anymore) i knew when the spell wouldnt work so that turn i just used an offensive spell. anyway all i remember is my mage died and all i had left was my warrior so i just prayed (not literally) that he didnt kill my warrior off and i could attack at least 1 more time and get some critical hits in and thats how i won lolz.
I experimented using this method and forgot exactly which way worked but that was the major factor...i would try changing things like revive a character just so it would take hits instead. it was somethin similar to what i said above tho. its a risky method but if u try it good luck u will need it =P (not sure about my level i think i was in the 60s. =P)