Hako no Naka no Itsuka no Umi

While cleaning up the family Buddhist altar, Akari finds her great-grandmother's box. When she removes the double bottom, she finds an old marriage certificate and a wooden box. There is an unfamiliar name on the marriage certificate. It doesn't belong to her great-grandfather! Unable to wait any longer, Akari travels to Shikoku to investigate the mystery. Together with her distant relative Ryo, she gets closer to the secrets of her ancestors.

(Source: Comic Days)