Sebastian is one of the villains from Blood Omen 2: Legacy of Kain.
Sebastian was one of the vampire lieutenants of Kain, who had started a coup to take over Nosgoth. Unsatisfied with Kain's rule, Sebastian betrayed him and sided with the Sarafan Lord, arranging an ambush that ended with Kain being defeated by the Sarafan Lord. The two would meet again in the reformatory, as Kain was looking for the sanctuary of the Cabal. Kain saw a lot of human corpses on the grounds, witnessing Sebastian killing a human. Kain couldn't recognize him due to his amnesia, but Sebastian tells he knew him, and although he would enjoy killing Kain, he had more important matters to attend. Sebastian flees, so Kain gives chase to him, eventually catching up to him. Kain asks if he serves the Sarafan, but he simply replies that he serves no one but himself, leaving Kain.
Some time later, Kain goes to the Quarter looking for the Nexus Stone. When Kain enters the chamber where the stone was, Sebastian welcomes him. Kain finally recognizes him, challenging Sebastian for a fight. The room had steam jets controlled by a human in a room above. Kain tried to knock Sebastian into the steam, but Sebastian started to run around the room above the steam by using his berserk ability, attempting to swiftly strikes Kain from a distance, but Kain tricks him into falling into the steam, burning him. Sebastian orders the human to rise the central platform so that he can destroy the Nexus Stone.
Kain jumps on the platform to stop Sebastian, who goes down to take cover from Kain. Kain mind-controls the human to fill the room with steam, forcing Sebastian to jump on the platform and fight Kain. Kain wins, knocking Sebastian into the steam, which burns him severely. Kain demands answers, so Sebastian tells him the Sarafan have unearthed The Device, which will allow the Sarafan Lord to exterminate all of his enemies and complete his rule over Nosgoth. Sebastian dies shortly after, so Kain takes the Nexus Stone and leaves the place, which starts self-destructing.