Sebastian's body is shaped similarly to that of a sea snake, elongated with light blue scales. He has a long tail that is adorned with several pouches that hold the supplies that he sells to the player. At the end of his body is a large tail fin. He has three arms, one of which is attached to his left side and is wrapped in a bloodied bandage. His hands are humanoid, yet only have four fingers and are claw-like. Sebastian's face retains a humanoid appearance with fish-like features, such as an anglerfish esca on his forehead, fin-like appendages in place of ears, a fish-like mouth, and a third eye on his right side. He has black, short, wavy hair.

him wearing a dark brown jacket with a white undershirt and white jabot. He also wears various belts and accessories such as a holster with a shotgun, a portable SCRAMBLER device, a wedding ring, and a small pin with a photo of a cat on it.

Sebastian can be described as snarky, unpredictable, and violent at times. He has grown to deeply hate Urbanshade due to their experiments on him, thus, actively seeks to harm the company. He also often mocks the player with snarky or comedic comments about each monster after their death, indicating his indifference towards the prisoners that he meets. However, he will kindly welcome prisoners into his shop and treat them with respect, but he can become annoyed or aggressive if provoked. Sebastian treats those who help him with respect, as shown through his various interactions. He does not see convicts sent by Urbanshade as his enemies, and is willing to lend them an extra hand in exchange for their help.

In 2013, Sebastian was falsely charged with the murder of 9 people, being sentenced to execution. Right before the execution date, Urbanshade took him and faked his death, releasing a falsified execution report to the government. He was then imprisoned as an LR-P rank prisoner in the Hadal Blacksite.

In early 2015, Sebastian was chosen for an experiment designed to give humans fish-like gills in order to allow them to breathe underwater, experimenting with various DNA samples of deep sea creatures. While the experiment succeeded in giving him gills, it mutated his appearance beyond recognition. Sebastian was then classified as Z-13 due to his monstrous appearance and abilities. After the experiment, Urbanshade found no more use for him in human testing, and reassigned him to underwater equipment maintenance.

Seven months later,[3] Sebastian was found to be not guilty of the murders he was accused of. This information was not shared with Sebastian, nor was he released from his imprisonment. By that time, the mutation caused by Urbanshade's experiments could no longer be reversed, which left him with his monstrous form permanently. Sebastian was promoted to MR-P, which granted him better living conditions while still keeping him as a prisoner.

Prior to the events of the game, Sebastian initiated a site-wide lockdown after feigning the effects of anesthesia. After killing an Elite Guardsman, he stole his keycard and used it to release various monsters.

Sebastian is Chilean-American. Sebastian canonically smokes tobacco. Sebastian can play the electric guitar. His favorite music genre would probably be rock, and would like bands such as Metallica. Sebastian is a cat person. Sebastian likes sweet, spicy, and sour foods. Sebastian sees Kroner Kroner as useless and does not like delivering dead drops; insulting the player if he is forced to do a delivery. This does not apply if a player enters his shop to buy items using research found inside the Blacksite. Sebastian is planning to use any documents he scavenges as blackmail in order to leverage his way out of the Hadal Blacksite by trading them with rival companies. Sebastian doesn't actively seek out items to sell to the player; instead, he finds them by accident.

Male (he/him)

Age:35 Height:62'4 Birthday:February 3, 1993.