The Sea of ​​Yesteryear in a Box

While cleaning out the family altar at her childhood home, Akari discovers her great-grandmother's box. Removing the double-layered bottom reveals an old marriage registration form and a wooden box. The name on the marriage registration form is unfamiliar. It's not her great-grandfather's! Unable to contain her curiosity, Akari heads to Shikoku to investigate the mystery. Together with her distant relative, Ryo, she gets closer to uncovering the secrets of her ancestors.