The year is 2008, and Mikuru is a 16-year-old high schooler who often disagrees with her mother Yuki. One day a girl appears in front of her—"Yuki"—a cute girl who's thoughts, memories and body are from 24 years earlier. In short, Yuki has "time-slipped" from 1984 to the present, and when Yuki wakes up she is shocked to find that the year is not 1984, and that Mikuru is her daughter.
Now both mother and daughter are the same age and living in the same house together, with an older man who's supposed to be her husband. Until when she can return home, the girl who has crossed space-time decides to discover her future.