Hatsune grew up with the gentle Ken'ichi-niichan and the mean Kenji. Hatsune wants to become Ken'ichi-niichan's bride when she grows up, but he already has a girlfriend. Though, one day, she hears from Kenji that they've broken up. Time for her to launch attacks on Ke'ichi-niichan!

(Sorce: MangaUpdates)