SSNI-789 is an adaptation of the doujinshi 「家族が旅行で不在の間、娘の友達とハメまくりました」 (Kazoku ga Ryokou de Fuzai no Aida, Musume no Tomodachi to Hamemakurimashita), which translates to "While My Family Was Away on a Trip, I Had Sex with My Daughter’s Friend.". It was originally written by Yamanashi Musume (山梨娘).


The story follows a man who find