Slightly late on my way to work, I see my high school classmate, Misaki Niwa on the station platform across. Misaki herself, not someone with a good resemblance, just as she was in high school, still the same 18-year-old girl.

No one seems to find this strange, but only I, who was in love with her in high school nine years ago, can tell that something is amiss. Why is she staying eighteen years old - her senior year of high school?　

I start visiting friends and teachers, going back to our school days investigating why Misaki is stuck with her eighteen-year-old self.A fantastic mystery of remembrance by one of the most talented and popular writers of our time.