Sebastian is a middle-aged man of approximately 1.85 m height with shoulder-length dark brown hair and blue eyes. The only physical difference between Sebastian and his son is Sebastian's arched nose.
In Axel's flashbacks Sebastian usually wears a white suit with a black t-shirt underneath and sunglasses. During the training sessions with Axel he wears a martial arts training suit in dark blue with orange hems.
Little is known about his personality since he only appears in Axel's flashbacks. He is a very caring and encouraging father who guides Axel into finding the answers to his questions. He is very intelligent, clever and wise, but also courageous and loyal towards his comrades.
Axel Manning - Axel is his only child and student of the arts. He took very good care of him when he was a child and prepared him for different physical and mental challenges. He also left behind his journal so that Axel could find out the truth behind his father's disappearance.
Unknown wife - Axel's mother. Her name and her current whereabouts are unknown. She has long blonde hair and blue eyes.
Alexander Paine - Sebastian's partner when a federal agent. At first it seemed that Paine had betrayed Sebastian, but it has been revealed that it was Sebastian who protected Paine from the explosion and saved his life. Since Sebastian presumably died in that explosion, Paine was accused of having killed his partner.
Janus Lee - Lee was the head of the Chrysalis Project which Sebastian was a security contact person of. He found out that Lee was selling government secrets to an organisation called "The Serpent's Tale", and the night he was confronting Lee about the matter, Lee told him not to dig into it and leave it be. But Sebastian decided to bust "The Serpent's Tale" and found their meeting place which they later blew up, presumably to destroy any evidence. After this incident Lee quit the project and blamed himself for Sebastian's death.
Sebastian has been trained under Master Ji and can be considered a master of the arts himself. It is not known what level he reached since he is only seen using the blue spiritual power when training with his son.