The live-action drama follows teenager Shota Sekiguchi, whose family runs a small struggling sushi shop called Tomoe Sushi in the port city of Otaru, Hokkaido. Their business is being driven to the brink of ruin by Sasa Zushi, a massive sushi chain that uses aggressive pricing and bulk purchasing to dominate the market. Adding to the family's hardship, Shota's mother suffers from an incurable illness, draining their savings and leaving his father unable to work consistently.

When his father is injured and cannot compete in a local sushi competition, Shota takes his place. Though he does not win, his natural talent and dedication impress one of the judges, Seigoro Otori, the owner of the renowned O Sushi restaurant in Tokyo. Otori offers Shota an apprenticeship, and his father agrees, recognizing that his son must gain broader experience to have any hope of saving the family business.

In Tokyo, Shota quickly discovers that becoming a true sushi master requires far more than simply knowing how to prepare tasty fish. At O Sushi, the two most senior disciples, Masaji Fujita and Hidemasa Okamura, are welcoming, but the third disciple, Yasuto Saji, is a jealous bully who torments both the newcomer Shota and the youngest apprentice, Shingo Obata. Master Otori observes the growing rivalry between Shota and Yasuto and decides to harness it as a teaching tool. He announces a three-round contest between them to determine who will represent O Sushi in the upcoming Tokyo sushi competition.

The first round features sea bream, deliberately chosen because it is out of season, forcing each contestant to source the fish themselves. Shota's friends manage to find one for him, but Yasuto steals it. Forced to use an inferior subspecies, Shota nonetheless wins the round by employing a superior cooking technique, a defeat that deeply humbles Yasuto and forces him to reconsider his approach to life and cooking. The second round focuses on unagi, or freshwater eel, an ingredient that heavily favors Yasuto. He reveals that he has been brewing his own eel sauce for three years, a crucial component of the dish that traditionally takes years to develop. Shota innovates a sauce-free preparation that is delicious, but he loses the round after failing to answer a critical question about the proper order of serving dishes.

For the final round, contestants may choose their own ingredients. To encourage the disheartened Shingo, whom Yasuto had cruelly compared to a lowly anchovy, Shota deliberately selects anchovy. He wins the round, and despite losing the overall contest, Yasuto has matured tremendously. Master Otori offers Yasuto a promotion to man a counter at the restaurant, but Yasuto declines, choosing to continue his training elsewhere because he fears his growth would be limited if he remained alongside Shota. He swears to Shota that they will meet again for a rematch.

The story then follows Shota as he enters the Tokyo sushi tournament, learning new lessons with every round and refining his craft against a series of talented rivals. Throughout his journey in Tokyo, he must also contend with the ongoing crisis back home, where Sasa Zushi continues its relentless campaign to destroy his father's small shop, adding constant urgency to his quest to become a master sushi chef.