While her husband is away on business, Sei lives with her daughter and her husband, who are trying to save up money for a home. They are happy, but as they get older, their libidos increase... One day, she finds out that her son-in-law Kenichi is spying on her masturbating. Sei is turned on by his big, powerful dick and tries to seduce him all the time. Kenichi, who is sexless with his wife, cannot resist her seductive behavior and repeatedly ejaculates into his mother-in-law's body with his enormous cock. Before he knows it, Hijiri can't live without his Sei dick...