Man-sik Sul Kyung-gu is a local from the Haeundae district of Busan who, during the 2004 Indian Ocean tsunami, unexpectedly loses Yeon-hee's father while aboard a deep-sea fishing boat. A series of past misjudgments leads him to withdraw from Yeon-hee and her uncle, Eok-jo, who once acted as a shipowner that allowed Yeon-hee’s father to set sail in dangerous conditions. The tragedy casts a long shadow over Man-sik’s life, and he finds himself keeping distance from Yeon-hee even as she grows into adulthood.
Yeon-hee Ha Ji-won has since built a life around an unlicensed seafood restaurant. She longs for a connection with Man-sik, hoping to share something meaningful after all they’ve endured, and she carries the weight of the past with quiet resilience. Her world begins to shift as she contemplates love, even as redevelopment plans cast a looming threat over the beloved seaside neighborhood she calls home.
Dong-chun, Man-sik’s half-brother, becomes entangled in illicit schemes with his son Seung-hyun, drawing the family into danger and a clash with the authorities. This turbulence bleeds into Man-sik’s life, fueling tensions and forcing hard choices about loyalty, family, and survival. Meanwhile, Eok-jo—now Busan’s head chairman—presses a bold redevelopment of Haeundae into a special tourist zone, stirring backlash from locals who fear displacement and loss of community.
In the midst of the chaos, Kim Hwi, a geologist, encounters his ex-wife Yoo-jin Uhm Jung-hwa and learns they have a daughter named Ji-min. Yoo-jin has started a new life with a boyfriend named Hae-chan Hae-chan, but she and Hwi decide not to tell Ji-min that Hwi is her biological father, worried about how she might react to the truth. The family dynamic becomes a delicate braid of love, secrecy, and the unspoken longing to belong.
Meanwhile, a chance connection forms on the other side of the city as a wealthy Seoul student named Hee-mi Hee-mi is saved from the sea by Hyeong-sik Hyeong-sik, Man-sik’s younger brother and a lifeguard. Hee-mi’s anger at the perceived roughness of the rescue gradually softens, and the two begin to grow closer, complicating Man-sik’s own feelings as he contemplates a proposal to Yeon-hee.
During a festive fireworks display, Man-sik musters the courage to propose to Yeon-hee. She signals her consent by hanging a ribbon outside her restaurant, a symbol that seems to promise a future together. But the next day, with the ribbon conspicuously absent, Man-sik’s hope is shaken. A chance encounter with Dong-chun reveals that he’s told Yeon-hee why her father died years earlier, a disclosure that fuels a dangerous misunderstanding and a brutal confrontation. The moment is underscored by a flock of birds taking to the sky, a eerie, almost prescient sign of impending disaster.
As Kim Hwi senses something ominous in the water—the same pattern of activity he observed before the first tragedy—officials dismiss his warnings, claiming the East Sea is safe. Yet nature has its own plan: a massive megatsunami is formed by a landslide off Japan and begins racing toward Busan. With only minutes before the wave reaches the city, panic erupts, and people scramble to escape. A minor aftershock rattles the coast just as the sea pulls away, and a wave of fear, awe, and urgent determination sweeps through the towers and beaches of Haeundae.
In the brutal rush to evacuate, many are caught on the Gwangan Bridge and swept away as the ocean roars inland. The tsunami drowns thousands, including Eok-jo who sacrifices himself to save Man-sik, and the bridge ultimately buckles and shatters, sending cargo containers and debris into buildings along the shore. On the rescue front, Hyeong-sik dives from a helicopter to save Hee-mi in the rough seas, choosing to sacrifice himself in a moment of heartbreakingly human courage when the rope between him and Jun-ha threatens to fail. Meanwhile, Yoo-jin, trapped in a flood, speaks to Ji-min on the phone as a coworker helps pull her toward safety; on the rooftop, Hwi finds his daughter and, in a tearful moment, reveals that he is her biological father, a truth that binds the two at last before the second, even more devastating wave arrives and claims their lives.
In the wake of the catastrophe, a solemn memorial service honors the thousands lost—including Hyeong-sik, Hwi, Yoo-jin, and Eok-jo. Dong-chun learns of his mother’s death and breaks down in grief, while the city begins the long process of rebuilding. The narrative returns to the surviving lovers as Man-sik cleans the ruined streets of Yeon-hee’s restaurant, discovering the red ribbon that once symbolized a promise kept. Hope lingers amid the wreckage, as a rebuilt Haeundae rises from the sands with a quiet resolve to start again, and the film closes on a tableau of a landscape scarred by tragedy yet touched by resilience and renewed faith in tomorrow.
