Sebastian lives with his mother, Robin, along with his step-dad Demetrius and half-sister Maru. Robin sometimes calls him Sebby. He feels that Maru is treated better than he is, and during Winter will talk about building a snow-goon that Demetrius demands he removes; he will then angrily question what his step-father's problem is.

Sebastian is good friends with Sam; the two can be found hanging out at Sam's house or at The Stardrop Saloon playing pool. They also stand together at festivals, along with Abigail.