Vasedra is an eredar void knight, a former death knight bound first to demonic powers and then, through those, to void powers. Her strengths are physical fighting with dual swords and manipulation of voidfrost as an offensive weapon.
Sedra was a simpler creature a few short years ago, a reborn draenei death knight called 'Sedrai' who became associated with the Netherbane and embroiled in their struggle against a Nathrezim known as Xonath. While they were successful in ending his threat, her involvement got her the attention of one of Xonath's peers and set in motion a sequence of events that eventually led to her being taken and bound to a trio of demons in a reversal of the demon hunter bindings.
For a time, she was a hidden agent of the Shadowed Sun Lieutenant, Malfias, on Azeroth, but eventually she was pulled to pursue more interstellar tasks.
Four years later, she returned with the Legion invasions, now a mostly amalgam soul built around the core of what had once been Sedrai. The death knight's wishes and will were isolated, imprisoned, by a piece of crystaltech of her own devising, but the concerted efforts of her friends have freed that last part of her. And just in time to stop her from doing the same to half of Azeroth.
Now, she serves Ary Valryss and the Netherbane as she struggles to understand and develop what she is.