A seemingly unremarkable man called “Mouse” is caught by the police. In exchange for his freedom, he goes undercover, infiltrates a drug ring, and arranges a fake deal, but an unexpected turn of events occurs.

Chiikawa and friends set off on a whimsical summer adventure to a mysterious island said to hide a long-lost mermaid secret. What starts as a fun getaway quickly turns into a heartwarming journey filled with surprises, gentle thrills, and adorable chaos. With sparkling seas, strange legends, and unforgettable encounters, the trio learns about courage, friendship, and the magic hidden in small moments.