Sebastian is an Arcadian Drakos, grandson of Lycaon. When he was younger, his cousin Percy was kidnapped by Katagaria Slayers who forced him to lure Sebastian away from his sister Antiphone. While he was away, they raped, then murdered her. Sebastian was exiled from his patria for not protecting her. Sebastian lived on his own for centuries, but still upheld his oath as a Sentinel.
In the story "Dragonswan," Sebastian traveled to a museum in the future to retrieve the Dragon Tapestry. Slayers had kidnapped his brother Damos, thinking he held the tapestry, then demanded that Sebastian give it to them in exchange for Damos. At the museum, he met his mate Channon, a history professor who studied pre-Norman Britain, which is when and where he lived. He took her back in time with him and she was attacked by Slayers. Sebastian was poisoned with Dragon's Bane while rescuing Channon, but he recovered by Claiming her.
The Katagaria who had kidnapped Damos admitted to him that they had tricked Sebastian into leaving Antiphone alone to be brutalized. Damos and the whole patria realized that they had misjudged Sebastian and revoked his banishment.