Located on the upper side of Kinmon Gate, this riverbank is where the souls of the deceased gather. Sai-no-Kawara is on the banks of a mythological river in the netherworld where children who have died before their parents are said to gather. While praying for their parents there, the children themselves build stupas out of stones to accumulate merit for their salvation. Whenever they get close to completion, the stupas are knocked down by the demons from hell and they have to start over. The children will be released from their suffering when Jizo Bodhisattva comes to save them.
This belief reflects the Japanese culture of the time when it was considered a grave sin to die before one’s parents.
You might see some stone stupas now, but when the river rises, it will wash them all away. It is thought that the wild flow of the water is connected to the demons of hell, leading to the belief of Sai-no-Kawara.
Particularly in Daisen, the riverbank is also believed to be the place where people can meet their ancestors. The riverbank is located inside the Kinmon Gate so that the gathered souls can be within Jizo Boddhisattva’s reach and be comforted.