Yuna has recently grown increasingly dissatisfied with her husband, left chronically frustrated and unable to sleep. Living under the same roof as her daughter and son-in-law Takayuki, she notices he's neglected by his wife and discovers him masturbating every night. Shocked by his thick, massive cock, Yuna can no longer suppress the lust rising from deep within her body. Under the pretense of "taking care of him," she begins servicing his huge shaft around the clock. Drowning in the pleasure of his enormous cock, the stepmother obsessively indulges her carnal desires, and as their depraved affair intensifies, her son-in-law increasingly unleashes his overflowing sexual energy on her.