After five years of marriage, Jun's relationship has gone stale and sexless. His wife refuses him, and the serious, reserved man cannot bring himself to visit a brothel. When his wife leaves town for three days, her equally sex-starved older sister Saki stops by with food and learns about their dead bedroom. She seduces the frustrated younger man, and while her sister is away they devour each other's bodies. Claiming that being in-laws means it is not really cheating, Jun loses himself in Saki's ripe body and cums again and again.