Eberron: Unsung Heroes
Tannis Sol is Kerra’s old rival, a fellow student of the master of arcane that trained them both.
Tannis appeared in Sharn when he apparently kidnapped Raine, trying to draw out Kerra. He did, and he invoked a ritual that warped the man’s mind and gave him arcane power. Tannis teleported away from the fight before he could be involved, but promised Kerra an “eventual showdown.”