The story centers on a pair of stepsiblings. When Kōta's father gets remarried, Kōta's first impression of his new stepsister Aika is that she is beautiful, but that image is shattered pretty quickly. His new stepsister 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.