Wakaba Himekawa is aware that she is growing up more slowly than other people, but otherwise lives a peaceful life.

On the same day that she finally gets her first period, her childhood friend Takaya confesses that he loves her. While Wakaba had never felt that way for her friend before, she is still happy, if confused. As she is about to answer Takaya confession, an alarm suddenly sounds, and a broadcast begins that will change her everyday life.