Sebastian has short, blonde hair, brown eyes and light skin. He wears a blue jacket, a yellow pull-under, a white shirt and a red tie.
Acting is Sebastian's passion. Playing the rogue is his specialty, which makes him prefect for the role of Lord Rathbone in James's play. According to James, Sebastian is something of a "textbook narcissist" and has "delusions of grandeur" and also believes himself to be superior to Chris and his friends because he went to a prep school while they went to public school. He has even tried to bribe Chris into dropping out of the student council election. He is also guilty of embezzlement. He is racist against Latinos. He isn't worried to show his dark side as he violently grabbed Your Character in public.
Sebastian and James know each other from prep school. The upperclassman describes him as a talented actor and textbook narcissist with delusions of grandeur. They seemed to be friends but James is very disappointed how Sebastian treats the not-wealthy students and mentions, that he was different back in prep school. After this, James turns his back on Sebastian and supports his rival Chris at the campaign.
Sebastian was running against Chris in the Student President election. He thinks that Chris and his friends are inferior to him because they are not as wealthy as him. He has tried to bribe Chris into dropping out of the election but Chris refused. He is currently the treasurer of the student council much to Chris's shock and horror. He is shocked then Sebastian is willing to make a racist comment against Latinos as if it's no big deal.
Becca and Sebastian meet at the audition of James's play. She got fed up with the fact he never took her out on dates and never complimented her. She dumps him at the end of Book 2.
From the beginning, Sebastian has never really liked Your Character. He immediately insults her and everyone else's acting, showing his narcissism. He has a tendency to bicker and start arguments with the young girl, during which, he talks to her in a derogatory and condescending manner.
Zig has stated he doesn't like bullies so he logically despises Sebastian. Sebastian immediately makes a comment on how Zig probably just got out of jail and is working as a barista,this is racist as Zig is Latino. Zig tries to walk away but Sebastian immediately sticks out his foot to trip him. This leads to Zig punching Sebastian in the face hard enough to knock him to the floor.
- He bears a resemblance to actor Eddie Redmayne.