"You act like this is our first time together." We had only just met when my neighbor Kamiya said that to me... - Shii Hayama, 27 years old, is an office worker at an advertisement company. With the intense workload she has, taking the last train home late at night is just part of her routine. One such night, a man she doesn't know wakes Shii up after she drifted asleep on the train. She later discovers that this man was her new neighbor, Azusa Kamiya. Even though they've just met, how is it that he knows her body inside and out?! This Kamiya guy is hiding an astonishing secret...!