"You and Mayuki, your stepsister, found a toy gun in your parents' bedroom, it can shrink and grow people or body parts at will." "Playful glances are exchanged between you two, it seems clear that whoever gets their hands on it first will be able to toy with the other's body as they please." Mayuki: "This is gonna be a wild ride." "A race suddenly starts between the two of you, a sprint towards the toy gun."