Nanami and Sakura are best friends. Nanami is the elder sister who is strong-willed and dependable, while Sakura is the reserved, but lovely little girl, who has a mega bust that is disproportionate for her petite body. They are friends from school, but they also have a connection through their families. On her days off, Nanami goes for a drive with Sakura's father, Shouhei, and he treats her like another daughter. This makes Nanami wish that he would marry to her mother, Kanako. That's how much she trusts him.
That is until...
"What are you doing...?" In front of her isn't the fun and nice uncle that she's used to everyday, but a primal fiend who has no sense of logic as he rummages through Sakura's room.