The story centers on a pair of step-siblings. When Kōta's father gets remarried, Kōta's first impression of his new step-sister Aika is that she is beautiful, but that image is shattered pretty quickly. His new step-sister is a super sassy and foul-mouthed gyaru who behaves uncontrollably while their parents are away, making Kōta's life a living hell. However, their relationship begins to change when Aika gradually warms up to Kōta's caring older-brother nature.