Out of the blue one day, schoolgirl Miki Koishikawa's parents announce that they are getting a divorce. During their trip to Hawaii, they met another married couple, the Matsuuras, and Miki's mom fell in love with the other husband, and Miki's dad, with the other wife, and hence the two couples are swapping partners and getting remarried. They also propose that the two families, including the Matsuura's son, Yu, who is the same age as Miki, move in together.As such Miki and Yu start living under the same roof with their unconventional parents. In contrast to Miki, who wants to maintain a certain distance from her off-the-wall parents, Yu seems unfazed by the whole situation. Miki starts falling for Yu, who she discovers has a kind heart under a cool exterior. Then one day, Ginta, Miki's former crush who rejected her while in middle school, confesses that he'd always had feelings for her. And Arimi, who claims to be Yu's ex-girlfriend, also enters the scene...