The Japanese Buddhist tradition / folklore equivalent of the River Styx in Greek mythology. Datsue-ba and Sai-no-Kawara (Riverside of Sai) are both related to this river.
Unlike Charon in Greek mythology, the name of the ferryman of the river is unknown. This is because according to old legend, the dead did not cross by boat, but they walked across the river on foot. The only thing that is known is that the fee for the ferryboat was rokumonsen (six mon coins), this is why on the Japanese (Buddhist) version of joss papers there is a drawing of six mon coins. This symbol was also used as Sanada clan's emblem.