12-year-old Oriko Seki, who lost her parents in a car accident, ended up living in her grandmother's Onsen Ryokan "Haru no Ya." With the ghost "Uribou" cohabitating with her and all the other odds, she ended up training to be a young female innkeeper. At first, she didn't like the training, but gradually felt her admiration for her title and began to train seriously. Thus, the growth of the young warrior Oriko begins.

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.