In Hayashigakure City, a city in the mountains, is a dark ceremony which has continued for thousands of years.
In order to appease an angry god, the men gather to engage in group sex with a girl designated as a shrine maiden — if the girl becomes pregnant, then the god shall be appeased and bless the village with peace and a good harvest.
The pregnant girl is then wrapped in straw soaked in the semen of the men and set adrift down a river to become a sacrifice to the god.

In the present, the ceremony has not been forgetten to the depths of history… the depraved and wretched ceremony is continued by a secret organization, the Group Sex Club, at the only school in Higashigakure City.