Bahamut uses Megaflare, but it can be reflected.
Rosa and Fusoya should cast Reflect, and other members use any items to cast walls. It is best to cast Reflect on Fusoya and Rydia first, and then cast it on members with the lowest HP. When Bahamut uses Megaflare it will reflect back onto him. The Reflect wall will last two uses of the Megaflare before the player must re-cast it. Recasting it when the Reflect wall is still up will cause it to bounce to Bahamut. It is possible to win the battle by simply allowing Bahamut to kill himself, applying magic only to the player party.
If the party has no Reflect items or Fusoya, winning is harder. Before the battle the player should kill all party members but two, Rosa and another character. This is needed because Rosa is usually the last to take her turn, so by killing off two characters Rosa will definitely get a turn in before Bahamut uses Megaflare and can cast Reflect on herself. If the other member survives Megaflare, Rosa should cast Reflect on him, if not, just leave them knocked out. When Bahamut uses Megaflare again, Rosa should re-cast Reflect. The player will still win as Bahamut will kill himself.
In the GBA and PSP versions, the above strategy works, and Porom would also be recommended for she can also learn Reflect. Rydia or Palom can help by casting either Tsunami or Quake, but it is possible to take Bahamut out with just one character: Kain Highwind.
Kain should Jump at Bahamut between the count of 3 and 2, and he will land right after Bahamut casts Megaflare. The player does not need to bother to revive the other members, as they will not survive most of the time.
Bahamut (Arabic بهموت Bahamūt) originated as an enormous whale in ancient pre-Islamic Arabian mythology. Upon Bahamut's back stands a bull with four thousand eyes, ears, noses, mouths, tongues and feet called Kujuta (also spelled "Kuyutha"). Between each of these is a distance of a 500-year journey. On the back of Kujuta is a mountain of ruby. Atop this mountain is an angel who carries six hells, earth, and seven heavens on its shoulders.
Another version of the Arabic story is that Bahamut is indeed a dragon and he stands on a whale called Liwash.
In modern times, the game Dungeons & Dragons is responsible for re-imagining Bahamut as the king of dragons, a benevolent Platinum Dragon; the opposite of the malevolent Tiamat, the five-headed Chromatic Queen of Dragons.