Summons aren't meant to be used like this! What happened to dreams and honor?
Bahamut is a boss in Crisis Core -Final Fantasy VII-. It can be fought twice during the game, once in the campaign and once in the second 'Dr Hojo' mission.
Zack should equip any Lightning-resistant accessories to minimize the damage caused by Bahamut's Lightning Bolt, Laser Orbs, and Megaflare. Lightning Bolt should be avoidable, but there is no way escaping Megaflare that will roughly deplete 500 - 600 points of Zack's HP. The player should use Potions or Cure to keep Zack's HP above 800.
Zack should attempt to land some critical hits or normal sword attacks to Bahamut while it is on the central rock area. It is impossible to deliver a sword attack when it is on the distant rock area, so the player must cast magic, Fire or Blizzard works. DMW and hit-and-run tactics will do well against this foe.
The second encounter is near-identical to the first and can be fought much the same way. However, Bahamut's stats are higher, and it also knows the spells Flare and Graviga, which it casts from the distant rock areas.
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.