The Seventh Sign: Mr. Sister

The Seventh Sign: Mr. Sister is a Japanese contemporary fantasy adult kinetic novel which tells the story of a man whose younger sister has begun to refer to him as her older sister following a divine incident which also caused a goddess's powers to be implanted in his body. The game features Japanese voice acting for all significant characters except the protagonist and contains explicit sexual content.

The story follows Reiji Aoba, a man whose younger sister, Erika, has begun to refer to him as her "onee-chan" (older sister), and if that wasn't strange enough, Erika has cat ears which seem to appear and disappear at random. This began following an incident where Reiji slipped and cracked his head open on the steps of a shrine while taking a walk with Erika, though Erika has no memory of the accident. Reiji owes his survival to Fuuko Nanahara, a cat-eared girl who claims to be a local goddess who saved Reiji's life by implanting three of the seven fragments of her divine powers into him. Unfortunately, Fuuko says that if the fragments are not returned soon, both Fuuko and Reiji will die. To make matters worse, the only method that Fuuko can think of to safely extract the fragments involves shaking Reiji's heart to its core. Reiji reluctantly follows along with Fuuko's plan, hoping that he can save their lives and turn Erika back to normal over the summer break.