SEBASTIAN
Sebastian's deepest truest goal is to be happy. In order to do that, he needs to destroy the embodiment of everything that ever went wrong in his life: Cait Blank.
From a very young age he was sort of a control freak--he insisted on coming up with all the rules for childhood games, and made sure to maneuver himself into always being the most popular kid in the class. He worked very hard at appearing to have no weaknesses throughout high school--valedictorian, varsity baseball captain, and all-around most popular student. For this reason, he felt like he was putting up a facade. The one concession to perfection he allowed himself was being best friends with Marcus. In high school, they were nearly inseparable. Sebastian thought that Marcus's acerbic attitude and general meanness made him a lot of fun to have as a friend. He also, though he'd never admit it, genuinely admired Marcus's conviction and sense of ethics; even though Marcus was a jerk, Sebastian thought that he was a good person. It helped that they'd known each other since middle school. He was, of course, friends with nearly every other person in the school.
His relationship to his family was complicated. His adoptive mother and father were exceedingly wealthy and relatively hands-off. He was never neglected, but he didn't feel that connected to them. When he was younger, he believed that his older sister and brother resented him. When he grows up he and his siblings reach more of an understanding.
College was fine for him. He excelled in classes and athletics, but put much less effort into maintaining his popularity, and was more isolated than he was in high school. Sebastian tolerated Todd, who he found abrasive, because Marcus was friends with Todd. The summer between freshman and sophomore year of college he traveled all over with both Marcus and Todd. Near the end of sophomore year, Todd and Marcus went missing. Sebastian believed that there was something beyond an accident at foot, and his obsession with the disappearance meant he ended up dropping out of college.
He did a bunch of "finding himself" (traveling), on his inheritance. He doesn't remember much of these years. He then started up a small convenience store mostly to have something to do with himself, partially at his parents' behest. They were sick of him doing nothing. Sebastian ends up becoming friends with Mila, who lives next door. I don't think I've ever made this clear, but a large amount what happens is that Sebastian and Mila go get brunch and yap. Sebastian loves getting brunch, and he loves yapping with his friends. It's his favorite activity. He's pretty happy with that for a few years, and in the meantime begins percolating this great theory of Cait Blank. This is only furthered when his parents get into a (nonfatal) car accident. Logically, he knows that random bad stuff happens all the time, but he can't let go of the idea that someone really is out to get him.
Todd calls him (Todd isn't dead!!!) and tells him that Marcus is dead(What!!!). This is the straw that breaks the camel's back, and sends Sebastian on a quest to bring Marcus back (you can do anything if you believe in yourself) and locate and kill Cait Blank, with the help of Casio(nerd), which will, naturally, restore the universe to its natural order of everything going well for Sebastian.