Hinako Mukaizumi is a 19-year-old who moves to an oceanside town to attend college and pursue surfing, with few concrete plans for the future. There, she is rescued during a fireworks display that sets her apartment building ablaze by Minato Hinageshi, a 21-year-old firefighter with a strong sense of justice. Hinako is drawn to his capable personality, and they quickly bond as he teaches her how to ride the waves, sharing moments of quiet confidence and shared stoke as they navigate the town’s shoreline together.
After telling Hinako that the best waves come after Christmas because a wish might come true, Minato heads to the beach the next day by himself and surfs without her, only to die while attempting to save a jetskier. This tragedy leaves Hinako distraught and she moves into an apartment away from the coast, trying to reckon with life without him.
As time passes, Hinako discovers that Minato appears in water whenever she sings Brand New Story, a song the two of them often sang together. While others cannot see him, they begin to spend time again, even in public, rekindling a fragile connection that challenges the boundaries between life, memory, and voice. Minato’s enduring presence unsettles him emotionally as he confronts his mortality—he cannot physically touch Hinako—and he faces a personal test when his coworker, Wasabi Kawamura, confesses his own feelings for Hinako. Minato asks Hinako to move on with her life, but she chooses to stay connected to his world for a while longer.
Hinako’s realization that she has become too dependent on him deepens when she prevents him from moving on to heaven, a moment that forces both of them to confront what it means to let go. Later, when Hinako visits Minato’s house, his sister offers her a window into what inspired Minato to become a firefighter and protect others. Hinako learns that she was the one who saved Minato from drowning when they were younger, a memory that binds their fates in surprising ways. Upon finding a drafted text on a phone, she reads the line urging her to “ride her own wave,” a message that spurs her to chart her own path.
Determined to carve out her independence, Hinako enrolls in a lifeguard training course, hoping to stand on her own two feet while continuing to surf. In the meantime, Yōko’s reflections lead her to confess to Wasabi, reminding him of how he inspired her to return to school during a period of bullying, a revelation that strengthens their own bond.
At Hinako’s part-time job, Yōko overhears the same group that previously set off fireworks planning another display at an abandoned building housing a large Christmas tree. The two trail the group to gather evidence, and the plan escalates into danger as the building catches fire. Hinako and Yōko are trapped, but Hinako calls on Minato once more; a powerful wave of water surges through the structure, extinguishing the blaze. They ride the wave on a backboard, sharing a final farewell with Yōko and Wasabi as Minato’s spirit ascends to heaven.
The next Christmas, Hinako, Yōko, and Wasabi—now dating—visit the Chiba Port Tower to celebrate Hinako’s lifeguard certification. As Yōko and Wasabi depart, Hinako sings to a fountain, but Minato does not appear. The tower holds a message he wrote for her the year before, and Hinako breaks down, holding the moment close. In the wake of these events, she continues her lifeguard duties and her surfing, choosing to honor Minato by living with courage, independence, and a renewed sense of purpose.
