Sebastian's body is shaped like a sea serpent, as it is elongated and has blue scales. At the end of his body is a large tail fin. Sebastian's skin is a light blue. His torso is humanoid, with two larger arms and one smaller arm on his left side. Sebastian's hands are humanoid, though he only has four fingers with claw-like ends. Sebastian's face retains a humanoid face (which is almost always smiling) with fish-like features, such as an anglerfish bulb on his forehead, fin-like appendages on his head, sharp teeth, a fish-like mouth, and a third eye on the right side. He also has a gold/yellow ring on his pinky finger (lower left arm). Sebastian wears a dark brown jacket with a white t-shirt and a white jabot. He also wears several belts and accessories, such as a holster with a pistol, a portable security device, a bandage around his smaller arm, and a small brooch with a picture of a cat. Sebastian's tail has several pouches containing supplies that he sells to the player.

According to his document, his first appearance in the pressure timeline is in 2013, when he is accused of murdering 9 people and sent to be executed in the electric chair. Before that happened, Urbanshade "captured" him and sent him a fake execution report, which ended with Sebastian being declared dead. In early 2015, he, now an LR-P rank prisoner, was chosen for an experiment to give humans gills. He was tested with DNA from a mutated anglerfish, ███████, a blue whale, a great white shark, a silver stickleback fish, a mantis shrimp, and a sea snake. While the experiment ended up being a success, the side effects were massive, such as in Sebastian's current appearance. There was a chance of reversing the physical damage done, but it wasn't necessary due to his low rank. He was now ranked as Z-13, for his monstrous appearance and more powerful abilities. Later in 2015, Sebastian was found to be innocent, as he did not kill the 9 people he was accused of. However, this information was not communicated to Sebastian or made public. Reversing the side effects was now impossible, but his rank was changed to MR-P, granting him better living conditions.

Sebastian runs a makeshift shop where he sells items and supplies to prisoners in exchange for any research they bring with them. He also supplies items to the player via Dead Drops , requesting crowns in exchange for items dropped off at the Underwater Dock . Sebastian does not view the convicts sent by Urbanshade as his enemies and is willing to help them in exchange for their assistance. The more times you leave and enter his shop, the angrier he will become, eventually kicking you out.

Sebastian can damage/kill the player by throwing a Flash Beacon at them. Upon doing so for the first time, Sebastian will pick said player up, say "Don't ever do that again", break his Flash Beacon, and throw them to the ground, dealing 50 damage to them. If any player proceeds to throw a Flash Beacon at Sebastian after the warning, he will instead pull out a triple-barreled shotgun and shoot said player, instantly killing them.

He loves being treated well, having things bought for him, being very kind, being respected.

He hates people who yell at him, treat him badly, bother him with the window, break his patience, and bother him with the Flash Beacon.

Date of birth: February 3, 1993 Nsfw?: Since he's almost amphibian/reptile, he might have two dicks, lero lero lero.