Kim Young-sook is a hardworking, pragmatic diver from Jeju Island. She begins her training as a baby diver in 1938 alongside her best friend, Han Mi-ja. She possesses a sturdy build and feels a deep allegiance to her community's matrifocal traditions, where women work the sea and men manage the household. In 2008, she is a stubborn elder who refuses to discuss her personal history.

Han Mi-ja is a beautiful, petite orphan carrying the heavy social stigma of being the daughter of a Japanese collaborator. Raised by a harsh aunt and uncle, she finds refuge in her deep friendship with Kim Young-sook. She lacks self-assurance and carries intense guilt over her mother's death in childbirth. She commemorates important moments by making charcoal rubbings in her late father's reference book.

Sang-mun is a handsome local man who helps his father manage a cannery in collaboration with the Japanese colonizers. He operates outside the traditional matrifocal norms of the haenyeo culture, maintaining a strict, patriarchal household. He holds frightening authority over his family and aligns himself with whatever political power controls the island.

Jun-bu is the son of the diving chief Do-saeng and a former childhood playmate of Kim Young-sook. He studies in Japan to become a teacher and represents an ideal partner in the haenyeo community. He is kind, considerate, and shares household responsibilities, encouraging his wife to follow her passion for the sea rather than remain at home.

Do-saeng is an experienced haenyeo who eventually assumes the role of diving chief for her village. She is a resilient leader who manages the collective's territorial diving grounds and seasonal expeditions. She provides guidance to younger divers while managing the immense grief of her daughter's tragic diving accident.

Yu-ri is initially a chatterbox member of the diving collective. During an early dive, she is attacked by a large octopus and nearly drowns. The severe lack of oxygen leaves her permanently brain-damaged, altering her personality and making her dependent on her family for daily care.

Clara is a teenage tourist from Los Angeles visiting Jeju Island with her family. She bears a striking physical resemblance to her great-grandmother, Han Mi-ja. As a high school swimmer, she feels drawn to the ocean and actively seeks out Kim Young-sook to bridge the gap between their families' histories.

Yo-chan is the son of Han Mi-ja and Sang-mun. Growing up in a volatile household, he frequently moves to avoid political and social complications. He forms connections with the younger generation of Jeju Island, indirectly linking the estranged families back together.

Joon-lee is Kim Young-sook's youngest daughter and the brightest student in her local school. She shows no interest in following the haenyeo tradition, preferring to read books like the novel Heidi and interact with visiting scientists. She eventually moves to Seoul to pursue an academic career in sociology.

Min-lee is Kim Young-sook's eldest daughter. She follows in her mother's footsteps by training as a haenyeo and working within the local diving collective. She learns the harsh realities of the ocean early when she narrowly escapes a dangerous rip current during a dive.

Sung-soo is Kim Young-sook's eldest son. As a boy in a haenyeo household, he grows up in a matrifocal environment where men are expected to manage domestic duties rather than provide primary income.

Kyung-soo is Kim Young-sook's second son, bringing her household up to three children. His early childhood occurs during the island's strictest rationing and civil unrest.

Wan-soon is a young, inexperienced diver in the Hado village collective and Min-lee's best friend. Her brief career as a haenyeo is marked by local gossip regarding her associations with boys from the village.

Gu-ja is a seasoned haenyeo who takes on the heavy responsibility of leading the diving collective. She insists on safety protocols, such as moving divers to deeper water to avoid onshore winds, but struggles with the immense guilt that comes when accidents occur under her leadership.

Dr. Park is a Korean scientist leading a research team to study the extraordinary cold tolerance of the Jeju haenyeo. He conducts physiological tests on the divers and acts as a bridge between the isolated island women and the modern scientific community.

Dr. Oh is a local teacher who recognizes Joon-lee's exceptional intelligence. He actively promotes her education, securing her a spot in a middle school in Jeju City and helping her understand the government's strict educational rules.

Shaman Kim is the spiritual healer of the village. She is responsible for performing rituals that honor the ocean goddesses and quiet wandering spirits. Despite the government outlawing shamanistic practices, she continues to provide spiritual guidance and medical help to the haenyeo community in secret.