Sawatari Maiko lives happily with Kyotaro, whom she married after an office romance. One day, she discovers that Kyotaro has been meeting secretly with Yukino, an attractive older woman from their office, and suspects an affair. Yukino is a single mother. In reality, she's not a good mother and treats her only daughter, Azusa, harshly.
When Maiko witnesses Yukino being violent towards Azusa, she tries to protect Azusa, but both of them end up falling down the stairs.
When she regains consciousness, Maiko finds herself in Azusa's body...?!