Hinako Mukaimizu, a 19-year-old university student, moves to a coastal town to pursue surfing while wrestling with an undefined future. Outwardly carefree and relaxed, she masks depression and inner turmoil beneath a cheerful demeanor. Her physical traits—light brown hair tied in a bun, brown eyes, and a tall 175 cm frame—are complemented by casual orange-and-yellow attire and a yellow two-piece swimsuit for surfing.

Her life shifts when firefighter Minato rescues her from an apartment fire. Bonding over surfing, cooking, and shared moments, their romance blooms. Hinako’s unstructured surf lessons clash with Minato’s discipline, yet their connection deepens through a shared song, later central to her grief.

Minato’s sudden death during a mission devastates Hinako. She abandons surfing, isolates herself, and moves inland. Discovering his spirit materializes in water when she sings their song, she becomes reliant on these encounters, preserving his presence in a water-filled inflatable porpoise. This dependence erodes her independence as she avoids confronting her loss.

A pivotal revelation from Minato’s sister—that Hinako once saved him from drowning as a child—sparks change. Finding his unsent message urging her to “ride her own wave,” she enrolls in lifeguard training, symbolizing her shift toward self-reliance. During a climactic rescue, she channels Minato’s spirit to extinguish a fire, finally releasing him.

Rebuilding her life, Hinako resumes surfing, earns her lifeguard certification, and cultivates a supportive network with Minato’s sister and colleague. Though sadness lingers, she confronts challenges with renewed resolve. Water and waves mirror her evolution from loss to empowerment, cementing her journey from grief to self-actualization.