Tsubaki has started living with her daughter and son-in-law after her husband was transferred to another location. One night, she witnesses her son-in-law Takeshi, who has been refused sex because his penis is too big, masturbating. Tsubaki, who was sexless, is Kokoro by the power of his towering, huge penis... Tsubaki continues to seduce him day and night, telling himself that his daughter's incompetence is her fault. Eventually, Takeshi can no longer resist, and even though he knows that she is his stepmother, he devours her voluptuous and lewd behavior...