Jiiiii～

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...

That day, Aika was indulging in intimacy with her boyfriend Takahashi in her room as usual. However, a certain situation stirs trouble between them. To make matters worse for Aika, Kota, who had heard the commotion, shows up at the door. Aika tries to brush him off and send him away, but Kota makes a bold move that takes them both by surprise.