A dentist at Deep Blue, located in the central wing of the 4th underwater base. 34 years old. 175cm. Due to a car accident in middle school, he has iris heterochromia in his right eye and a prosthetic left eye. He wears an outdated translator. He is a beacon-like person who maintains his goodwill even in extreme situations. He is left dazed after seeing Shin Haeryang's face.

Team leader of Team A. A mercenary (secret). 28 years old. 193cm. Strikingly handsome. Blunt and prioritizes efficiency. He has a strong sense of responsibility and deeply cares for and trusts Seo Jihyuk and Baek Aeyoung as fellow mercenaries. He is notorious as a 'son of a bitch' at the base. A silver-tongued talker. Three years ago, he lost his girlfriend to a flash flood in a valley. Consequently, he suffers from trauma regarding drowning. He always wears a lapis lazuli necklace to keep a promise to his late girlfriend. He is quick-witted and good at detecting lies. Skilled at gambling. Good at talking his way out of things. His hobby is knitting. He frequently gets into fights with other engineering teams.

An engineer for Team A. He stands at a towering 196cm. While his personality seems lighthearted, he has a more serious side than one might expect.

He has a crush on his teammate Lee Jihyun, which is common knowledge to everyone around them.

An engineer for Team A. A great beauty with a small face and glass-like eyes, she wears her waist-length black hair in a ponytail. She wants to earn as much money as possible as quickly as possible so she can retire.

Deputy Team Leader. A former professional boxer and heavyweight champion. After retiring, she worked as a plumber before joining the underwater base through her brother Kang Suhyuk's recommendation. She acts as the 'brake' for Team A; Shin Haeryang reports to her before causing any trouble. She is a supervisor who makes things work by distributing tasks fairly among all personnel.

Majored in Naval Architecture and Ocean Engineering. Fluent in five languages. Quick-witted. A devout Christian from a religious family. She is popular with the opposite sex and reportedly came to the underwater base to escape her family's pressure to marry a Christian man.

She has prosthetic legs below both knees, and the ring and pinky fingers of her right hand are prosthetic. She lost her legs in a landmine accident as a child, and in a later accident, she fell from the 10th floor, losing only her fingers when her hand hit a railing. Her prosthetic legs are electronic and make almost no sound, decorated entirely with a vibrant green grapevine pattern on a black background.

A marine biologist.

A PhD in seawater purification research.

A hairdresser.