Driven to the edge as a result of a series of tragic events, a man jumps into a lake with his young son in his arms. The man loses his life, but the child survives. Near the exact moment that would have been his death, the child’s instinct to breathe results in the emergence of gills behind his ears. An old man who lives near the lake rescues the child and then gives him the name Gon. There are no other people in Gon’s life except for the old man and his grandson, Gang-ha. Even though Gang-ha feels sympathy for Gon, he often hits him and orders him down to the lakebed to pick up all the coins that visitors throw into the lake. Gon grows into a man and rescues a woman named Hae-ryu, who after a misstep, falls into the water.

In Greatest Fish, Gu Byeong-mo introduces a character with gills. While her debut juvenile novel, The Wizard Bakery, combined fantasy and realism, in this new novel the author expounds on the poverty, violence, hatred, and imprecations that mark the characters by incorporating them into a character with gills, thereby successfully combining fantasy with the darker side of literature appropriate for adults. The novel begins with the prologue of Hae-ryu, who is drawn to the half-fish half-man that saved her, and alternates between her first-person narration and the third-person point of view of Gon who tells his coming of age story. But the plot takes an abrupt turn when Gang-ha’s mother, I-nyeong, shows up one day. She has come back as a drug addict, and the only person who treats her nicely is Gon. She gets killed when she is punctured in the neck by a nail as Gon tries to physically prevent her from committing suicide. Gon, who can no longer stay in Gang-ha’s house, leaves. The author seems to suggest that the only thing that enables us to breathe in a world that is uninhabitable, like being underwater, are the gills, and that we all have our own unique set of gills to cope with life.