After four years of marriage, Kana and Masato are starting to see each other's hidden sides. Their arguments over trivial matters have been increasing lately... One day, they reunite with their high school classmate Tsubasa at their reunion. Back then, she was plain looking but has since transformed into a stunning beauty. Soon after, both Kana and Masato are invited by Tsubasa's husband to her house. There, they discover that the secret behind Tsubasa and her husband's happy marriage is swinging - exchanging partners with other couples.
