Selkie is a man with a muscular physique but with the appearance of a humanoid spotted seal that has a gray beard. He sports a full body wetsuit as his hero costume featuring yellow goggles, retractable flippers and a stylized "S" featured on the shoulder.
Selkie is a confident, kind, and professional individual who prioritizes his hero work and protecting his crew. He has a tendency to try (and succeed in) making himself look cute despite his macho appearance, much to the annoyance of his sidekicks. Even so, he can be quite stern when the situation calls for it.
Aboard the Oki Mariner, Selkie yells at Sirius and Tsuyu Asui for slacking off but apologizes using his cute persona after he finds out they have finished all their work. He and the crew later sail off to pursue stowaways who stole cargo from a trade boat. When they happen upon the supposed criminal ship, Selkie goes without Sirius and Tsuyu to investigate.
He and two of his sidekicks investigate the ship, only to be trapped inside by Innsmouth's lackeys. Selkie only returns to the action when Tsuyu relays an S.O.S across using Sirius's radio. Selkie finds Tsuyu and Sirius overpowered by Innsmouth himself. Innsmouth blinds Selkie using his ink, but Selkie uses echolocation to find and defeat him. Afterward, the stolen goods are returned and Selkie claims that Tsuyu will make a great hero one day.
Spotted Seal (ゴマフアザラシ Gomafuazarashi?): Selkie's Quirk allows him to do anything a spotted seal can. He can hold his breath for long periods of time and has above-human strength. He can also utilize echolocation when traversing dark waters or when his sight is hindered during combat, as seen during his fight against Innsmouth.