The narrative centers on the original cute animal-like characters Chiikawa, Hachiware, and Usagi, along with supporting figures such as Rakko, as they journey to an island troubled by a legendary Siren and mermaids. This central conflict reimagines the traditional Japanese Yao Bikuni ningyo legend of mermaid flesh granting eternal life, incorporating battery-powered immortality instead, and explores the accidental harm, desperate choices made by islanders Hitoha and Futaba, along with themes of revenge, guilt, and Chiikawa's empathetic decision to keep a secret.

These elements draw from classic moral ambiguity and folk horror traditions without any overlay of contemporary ideological framing. The film's themes revolve around courage, friendship, the consequences of folklore, and the magic found in small moments, remaining free from identity politics, systemic oppression narratives, or critiques of traditional norms. Produced in Japan with a standard voice cast and no statements from creators highlighting activism, DEI initiatives, or social justice messaging, the movie has seen reception centered on its box-office success and tonal surprise rather than any ideological debate. This approach keeps the focus squarely on entertaining storytelling rooted in established cultural motifs and character-driven adventures.