I was unsure about defender, as the multi-class feat only explicitly states that it opens you up for feats and paragon paths.
[sblock=Backgound idea]
Rhogar and Walking Dad's character were both members of a holy band of Seven Dragonborn, sworn to Bahamut's service called the The Vigilant. In the great celestial war we completed many different missions on behalf of Bahamut's 7 Gold-Dragon Exarchs and we were on the battlefield when Bahamut died. His death caused havok among the good side, and the initial press of the forces of evil was devastating. One of the last surviving Exarchs found the surviving members of the order amidst the chaos of battle. The Exarch gave one of us (probably Walking Dad's cleric) an orb which the Exarch said contained the remains of Bahamut's Divine essence--we were tasked with guarding it with our lives and keeping it from the forces of darkness. All seven agreed. The exarch left to continue the battle and guard our escape before any vile forces could determine that we had the last hope of Bahamut in our posession.
That was then. In the intervening year, the Vigilant have been haunted by the silence of Bahamut and his Exarchs. Every effort to discover what to do with the last essence has met with failure. When the Vigilant determined that another diety had also died, they decided to make their way to the site of Lolth's death to search for clues. Along the way, some force discovered what the Vigilant carried, and after countless attacks, only two of the seven tasked with the protection of the Last Essence survive. Hunted, they press on through the underdark, hoping beyond all hope that any success could ever come their way. Then, from beyond his grave in the astral sea, Bahamut smiles upon the last remaining members of the Vigilant, and they see a light in the darkness...a band of adventurer's, heading their way...
This aligns us with the other heroes, gives us similar motives, and explains how we still have our divine powers--through the Last Essence.[/sblock]