Mishakuji Otoshi

Takeshi Kanname is a college student majoring in Anthropology. He travels to a remote area of Japan for an assignment about fertility gods. Deep in the mountains, he stumbles on a little village that seems to have been plucked out of time long past. There is a festival celebrating the local fertility god when he arrives and Takeshi joins in hoping to gather data for his assignment. All the men line up to throw a straw ring at a stone idol in the shape of a phallus. Takeshi wins the "game" and finds out that he is now the living embodiment of the fertility god with a sex drive and "phallus" to match. However, the price of the power is the use of his left hand. If he wants his body back, Takeshi will have to keep having sex until the god is completely satisfied. Unfortunately, this fertility god hasn't had any for a loooong time...