Hako no Naka no Itsuka no Umi

While tidying the family Buddhist altar, Akari discovers a box belonging to her great-grandmother. Opening it, she finds a hidden compartment containing an old marriage certificate and a wooden box. The name on the certificate is not her great-grandfather's. Curious, Akari decides to visit Shikoku to uncover the truth. Joining her is Ryo, a distant relative, and together they begin to piece together the mysteries of their family's past.