The Oki Mariner Crew specializes in maritime missions, occasionally receive requests for help from the Japan Coast Guard. When they are not on a mission, their daily grind consists of training, patrols and cleaning the Oki Mariner ship.
The crew is made up of five members and their hero costumes are related to the sea: Selkie, the hero and captain of the Oki Mariner, wears a costume based on a diver's suit, while his sidekicks wear sleeveless sailor suits.
The Oki Mariner Crew is a fairly efficient group of heroes for offshore missions. Their ship has the means to explore and patrol the sea and the rugged shores of the Japanese archipelago, as well as board suspicious ships. By combining the ship's radar with the crew's Quirks they can detect the position of their targets.
Tsuyu Asui choses to do her Hero Agency Internships with the Okie Mariner crew because she wanted to work somewhere that would match well with her Quirk. Froppy spends most of her internship training and doing tasks to keep the Oki Mariner clean. Despite this, she maintains a good relationship with the hero Selkie and his sidekick Sirius.
One day, the Oki Mariner receives a request from Japan coast guard asking them to assist in apprehending smugglers. Although at first Selkie and several crew’s members fall into a trap, Tsuyu and Sirius manage to locate the smugglers' ship, saving enough time for Selkie to reach the location and defeat the villains.
Students in class 1-A have permission to participate in Hero Work-Studies. However, due to the increase in villain activity, the U.A. faculty members allow Hero Offices with proven track records of employing students in the past to be allowed to take on first-year students.