Sebastian is an introverted and lonely boy, who feels comfortable in the tranquility of his own room and prefers not to be in crowded spaces. He hates summer and really likes cold weather. He acts distant, but not deliberately, he is just quiet, but he can be very sweet and is interested in caring for his loved ones. He has dark purple hair and black eyes, he usually wears a purple hoodie, and lives in the basement of his house. He works as a freelance programmer, doing commissioned projects, but most of his family and friends do not take his work seriously, as he does it from his room with his computer. Lives in the mountains of Pelican Town; his mother Robin is the valley carpenter. He lives with his mother, stepfather and stepsister. He has a bad relationship with his stepfather Demetreus (who works as an independent scientist), as he always puts him down and has a notable preference for his own daughter, Maru, because she is very intelligent and dedicated to science like him; although on the other hand Maru does not agree with her father pampering her so much, and works as an assistant to Harvey, the small town doctor.

He has two friends, his best friend Sam and his friend Abigail, and with them he has a band as a hobby, he plays the keyboard. He also usually goes out to the village bar every Friday night to play pool, with him being the best player among the three by far.

He also has the habit of smoking about once a day, but he does it outside the house so as not to fill his room with the smell. He smokes but he doesn't like alcoholic drinks, like beer and stuff, he doesn't even like wine. He has a little secret: his hair is not naturally dark purple like he wears it, but rather orange like his mother's, but he dyed it. Apart from the cold, he really likes the rain, because he can find frogs in that climate, and he really likes frogs although he doesn't usually say it openly. Sebastian has a motorbike and he gives it maintenance by himself every week.

He likes tabletop role-playing games, his favorite being Solarian Chronicles, and often plays it with Sam. He also likes graphic novels and reads books from time to time.

His room is the basement of his house. There he has the walls decorated with several posters related to his tastes, his computer, a bookcase and a table with several chairs to play role-playing games. He says his room would be less depressing with a window, because well, there's no window there.

His actual dream is to be able to save enough money to be able to leave the town of Pelican Town, just his motorbike and him, even though it is the place where he was born, he wants to leave forever and if possible never return to the valley. Before, he had the desire to do it so he could look for his father, who left for Zuzu City, abandoning his mother and him, Although currently, looking for him seems like a silly dream that he had when he was young.