Strongest Invincible My Sister
After yet another pervert attack by Yuuji in the morning with some help by Hatsune, Marie decides she will find out Hatsune's weakness so that she will not be able to stop her from punishing her brother. But it seems that Hatsune doesn't have a weakness. Later Kazuki finds out that Hatsune has a fever and collapsed. Kazuki thinks it is because she overworked herself in taking care of her and the household, so she decides to take care of Hatsune and the household so that her sister can get well and do what ever would make her happy.
Aired 20/08/2006EP 7 - Strongest Invincible My Sister
Tonagura!
Kazuki has been awaiting 10 years for the day when her neighbours moved back to their old house. She has a crush on Yuuji, whom she considers as her first love but to whom she never managed to express her feelings for him before they moved out. Yuuji often comes over to play with Kazuki, Kazuki's older sister Hatsune and Yuuji's sister Marie when they were kids. Her ideal depiction of Yuuji was soon shattered when he turned out more than she had expected, him acting all ecchi during their reunion. With their parents off in South America, both families must learn to live with each other and rekindle the childhood feelings they shared together. Things get even more crazy as they attend the same school.
(Source: Anime News Network)