Sebastian is a rebellious and serious loner who lives in his parents' basement. He is Maru's older half-brother, and feels that she gets all the attention and adoration, while he is left to rot in the darkness. He tends to become deeply absorbed in computer games, comics, and science fiction novels, and will spend large amounts of time pursuing these pastimes alone in his room. He can be a little unfriendly towards people he doesn't know. He has a black eyes and hair.