Miki Koshikawa's parents suddenly want to get a divorce, but instead of the "normal" divorce, they want to swap partners with another couple. Soon Miki gets a new brother, Yuu, who is the same grade as her. Though at first he keeps teasing her, she starts falling for him, but he is soon to become her brother, what will she do now?
The manga is pretty short, but somehow they were able to keep coming up with new tribulations for Miki's and Yuu's relationship that keeps you glued on the anime.
