While struggling to make friends after his parents’ divorce, Koyomi Takasaki meets Kazune Takigawa, but apparently, they already have. Kazune reveals that she’s from World Line 85, an alternate universe in which she and Koyomi are lovers. But in a reality where moving between dimensions is natural, could Koyomi be the one from another world?
Still, they're all worlds 
that your choices can lead to.
Aber alle Welten beruhen
auf den eigenen Entscheidungen.
Aun así, todos los mundos
dependen de las elecciones.
Aun así, todos los mundos
dependen de las elecciones.
Mais tous ces mondes restent
la conséquence de vos choix.
Ma sono tutti mondi
 che coesistono dinanzi a una scelta.
Mas são mundos após escolhas.
Впрочем, всё это обусловлено
принятыми в жизни решениями.