Gilbert tells what is happened in the ten years that passed when Oz disappeared. Break tells him to go spy at the Nightray family, where he also could get information on the chain, Raven, and get Oz back from Abyss. Initially, Gil was hesitant about going with the Nightrays as Vessalius and Nightray households are rivals. In the end, he chooses to go with Break, and met Vincent. Upon their reunion, Gil reveals that he had no memory of Vincent, his younger brother. As he grew, he finally found a way to tame Raven, and ultimately establish a contract with it. This is how Gil gained his nickname "Raven". (thetvdb.com)