Kaa-chan no Tomodachi ni Shikotteru Tokoro Mirareta. The Animation

Shiori and Arisa are longtime best friends; while Arisa has a son named Naoki, Shiori is a hot widow without children. When Arisa goes on a company trip, Shiori is invited to stay over for a few days to look after Naoki. Having long craved the widow’s curvy body, Naoki secretly masturbates but is unexpectedly caught red-handed by Shiori. This incident ignites a lustful sexual encounter between the young man and the woman long deprived of affection.