The Deep Breath by Yuri Oh

"I’d rather die than become a sea woman." After her dream of settling down abroad falls apart, Haewon is forced back to Jeju, she starts having conflicts with her grandmother—the respected leader of the local female divers. Bound by the tragic loss of Haewon's mother to the sea, the two have spent years avoiding the painful memory that tore them apart. But one morning, Haewon takes her first dive into the ocean to face the truth.