Yui has lost her husband and lives with her step-son. Worried about her son, who has become withdrawn since his father's death, she continues to look after him. However, that's just a pretense. Even before her husband passed away, both Yui and her son had been aware of each other as members of the opposite sex. One day, while the two are on a trip, her son makes advances on her at a hotel, and although she tells him no, her heart is filled with joy. She takes her son's penis in her mouth and caresses her private parts, causing her to overflow with lust...