Tokyo, at present.
NASA announces the discovery of a new planet in the solar system, Emanon, where life might exist. The shocking news spread throughout the world, then a fad of the new planet emerges. Despite people's enthusiasm, abnormal weather events occur frequently.
Working part-time at a travel agency, Mika (Azusa Inamura) is doing her Masters degree in theoretical physics. Mika looks like an ordinary graduate student. As a matter of fact, she spends every day talking to Teru in her delusions while hunting men using a dating app to distract herself from the loneliness. Seeing Mika like this, her best friend, Shige (Seicho Yoshino), a gay man, and Takayama (Mutsumi Sato), her senior at her graduate school laboratory, are concerned for her.
One day, Mika suddenly experiences de-ja vu and meets a version of herself. Bird says that Emanon might have caused the parallel world to intertwine.
Three Mikas: one lives in a world where Teru disappeared; the second one lives in a world where she meets Teru and their romance begins; the third one lives in a world where Teru has already passed away. The worlds where the three of them live start to loop. Due to Emanon, some kind of errors occur in space and time.