When Bahamut would meet his demise at the hands of his nemesis, Zeleme, Bahamut would in fact get the chance to become one of the most powerful angels in the Celestial Realm, a guardian angel.
However, due to the demonic influences he was exposed to, he wasn't able to become a full guardian angel, but more of a demon-angel (demon-angels should never be confused with darcelians, darcelians are born halflings while demon-angels are more "created", like an angel or demon changing to the other realm, or instances like in Bahamut's case).

The glowing markings on Bahamut are in fact the scars he's recieved over the years.
He does have wings, in this picture I just showed the one for simplicity and to give an idea as to how they would look.

Bahamut's original sword, Dragon's Honor, is the sword of the dragon king, so when he stepped down, the sword was given to his son Orion. So when Bahamut needed a new weapon, he found the ancient sword simply known as "The Templar", an ancient sword that forged by the ancient race of Zenethians and blessed by both the Celestial Realm and the Demonic Realm.


Photoshop CS2.