All things began that day.... Tamaki Maiko was my childhood friend. She was too active and hanging around me regardless of my thought. I was always at her beck and call. Though she was noisy during recess, she fell into deep sleep during classes, and that made teachers embarrassed. I thought of these everyday lives, when she played with me and made a fuss with classmates, as natural. Therefore, I did not think it was a special occasion when I made the acquaintance with Marufuji Izumi in the train. ...Until that happened. The people had disappeared all of a sudden, though many people must have been there a moment before... Then I met with Retsuji Aya. The ordinal days began to collapse when I saw Aya, who had lived lonely in the uninhabited world. Strange things began to happen one after another. I wondered if this world was not real, even my memory was not real? At the same time, a mysterious girl Saegusa Mitsuki began to appear in front of me. She told me to stop looking for Aya, and to forget all. However, I want to see Aya.