Aika, the new younger sister of Kota Takamura from his father's remarriage, is a super sassy gal who bluntly calls her stepbrother “lame” upon first meet. Calling each other names, with each holding the worst impression of the other, they begin living under the same roof. But Aika would bring men into her room and get down to business whenever the parents were out. Kota is greatly troubled by her loud and clear moans, but then one day, something changes...