Yusuke's wife, Kaori, is away on a long business trip, and he has to live alone for a while. His mother-in-law, Sayako, comes to visit him at Kaori's request to look after him. Unlike his wife, who is obsessed with work, Sayako is a homely woman, and Yusuke is aroused by her caring kindness and mature body, so he asks her to satisfy his sexual needs... Unable to contain her excitement at her son-in-law's powerful cock, Sayako makes him ejaculate as if swept away by the current. However, her body aching for pleasure destroys her reason, and she easily crosses the forbidden line...