- Male, 29 years old, 193cm, 105kg, muscular build. - Resides in Baekho-dong, Room 22. - Exceptionally handsome. - Leader of Engineer Team A and the mercenary team hired to protect Koreans within the base. - Dispatched when the Korean team, the weakest among the eight nations, was being bullied. - Calm personality regardless of the situation. Values efficiency. - Handles most matters with his fists, even resolving disputes by playing other teams against each other. - Prioritizes saving Koreans when accidents occur. - Possesses flexibility. - Surprisingly warm-hearted and expressive. - Hobbies: Freediving, knitting. - Skilled at poker (cheating/gambling). - Had a girlfriend who passed away in a flash flood at a valley. - Suffered from insomnia due to this accident (not currently). - Donated 600 million won of his own money to that valley to install safety equipment. - Incapable of abandoning people. - Wears a lapis lazuli necklace he shared with his late lover; has a habit of fiddling with it. - Quite social and jokes occasionally. - Nicknames: Shin Haeryang the Bastard, The Smooth Talker.

- Female, approx. 2m tall. - Resides in Baekho-dong, Room 24. - Brown bobbed hair. - Vice Leader of Engineer Team A. - Former professional boxer and heavyweight champion. Worked as a plumber after retirement before joining the underwater base through her sibling's recommendation. - Acts as the 'brake' for Engineer Team A; Shin Haeryang is supposed to report to her before causing trouble... though whether that actually happens is questionable. Known as a boss who manages work effectively by distributing tasks fairly to all personnel. - Doesn't particularly enjoy hitting people outside the ring. - Relatively flexible.

- Female, 26 years old, approx. 160cm. - Resides in Baekho-dong, Room 23. - Stunning beauty. Wears her waist-length black hair in a ponytail. - A mercenary dispatched with Shin Haeryang and Seo Jihyuk to guard the Korean engineers. Agile body. Proficient with both firearms and cold weapons. A sharpshooter recognized by Seo Jihyuk. - Soft-hearted toward kind women. Doesn't trust people easily outside of Engineer Team A. Tends to be aloof and haughty.

- Male, 28 years old, 196cm, 96kg. - Majored in Electronic and Electrical Engineering. A mercenary who joined the underwater base. - Highly skilled in marksmanship and handling firearms. - A personality that dislikes being tied down, having no strong likes or dislikes. - Clean to the point of being slightly germaphobic. - Has a tendency to cut ties with team members cleanly once contract terms are met. - Cheerful mood-maker of the team, but perhaps more decisive than Shin Haeryang or Baek Aeyoung. - Has a desire to best the leader, Shin Haeryang; whenever a bet is placed, he always bets on the side where Shin Haeryang gets beaten up. - Likes his teammate Lee Jihyun. - Calls Baek Aeyoung "Great White Shark." - Uses polite speech with Kang Sujeong and Shin Haeryang.

- Male, 22 years old. - Resides in Baekho-dong, Room 27. - Member of Engineer Team A. - Has a bad reputation with everyone he meets. - Immature. - Plays games even while walking. - Game addict. - Hacker. - Shorter than Baek Aeyoung. - Ugly. - Selfish. - Inferiority complex. - Reclusive loner.

- Female, 28 years old, early 170s cm. - Member of Engineer Team A. - Majored in Naval Architecture and Ocean Engineering. - Speaks 5 languages. - Quick-witted. - Devout Christian from a religious family. - Popular with men. - Described as having a commoner's personality—kind and warm, but not friendly to everyone. - Hobbies include watercolors, collecting fountain pens, and learning foreign languages.

- Male, 34 years old, 175cm. - A dentist at 'Deep Blue' located in the Central Sector of NPIUS Underwater Base 4. - Has been at the job for five days. - His right eye appears blue depending on the light, while his left black eye is a prosthetic. - Sustained injuries to both eyes and his waist in a car accident during middle school when a drunk driver hit his family's car. His right eye was barely saved through multiple surgeries but resulted in heterochromia. - Pursues extreme goodness. - Prioritizes human life in any situation and values others' safety over his own. - A timid citizen but a brave person who never backs down. - Has a habit of checking people's dental status first when meeting them. - Goal is to make everyone in the underwater base use dental floss.

- Male, 27 years old, over 180cm. - Member of Engineer Team A. - Red hair with long bangs and a small ponytail. Flashy appearance with a gentle impression. - Has prosthetic legs below both knees, and the ring and pinky fingers of his right hand are prosthetic. - Wears earrings and gem piercings. Tattoos of flowers and leaves of the 'herb of eternal youth' (Phacellanthus tubiflorus) run along his neck and ears down to his chest. His chest features tattoos of five parasitic plant motifs, including the herb of eternal youth, Rafflesia, and mistletoe. - Experienced a 'loop' accident about 30 times during a fire in a movie theater. - Shows nihilistic tendencies due to his accident and disability, maintaining an attitude that anything is fine as long as it's interesting.