Meet Kalecgos at the Nexus and claim the Charged Scale of the Blue Aspect.
You have done much to empower the Heart of Azeroth, and I am proud that the dragonflights have lent their strength to your cause. It is now time for the blue dragonflight to do the same. When I first learned of the essences, I knew that some remnant of my dragonflight's power must be out there, coalescing where we were once strong. That is exactly what I have found. The Kirin Tor have isolated its signature at the Nexus, but only the wielder of the Heart of Azeroth can claim it.