A depressed kid finds a sea creature who doesn't care that he's depressed. The movie stops asking why that matters and just lets you watch them make music together, and suddenly you're not thinking about plot anymore. The animation moves like it's dancing, the soundtrack wraps around you like it knows exactly when you need to breathe, and by the end you realize you've been smiling the whole time without deciding to.

Kai drifts through middle school in a quiet fishing village, weighed down by his parents' divorce and the isolation that comes with starting over. Writing songs and posting them online is one of his few joys, while the feelings he has for his parents stay unspoken. When classmates Kunio and Yuuho pull him into their band and he reluctantly joins them for practice on Merfolk Island, everything shifts. There he encounters Lu, a mermaid whose carefree spirit and genuine joy seem to exist outside the world's complications. As Kai spends time with her, something unexpected happens: the walls he's built start cracking. He finds himself actually speaking his thoughts aloud, connecting with Lu in ways he never thought possible. Yet the villagers have long held that mermaids bring disaster, and friction between Lu and the town soon puts everyone in danger. The film blends music and fantasy, setting Kai's very real struggles against the magical presence of a new friend.