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?
So in the end, what you do is
 for you to decide, Koyomi.
Nur du kannst entscheiden,
was du tust.
Al final eres tú quien decide.
Al final eres tú quien decide.
En fin de compte, c’est à toi
de faire tes propres choix.
Alla fine sei solo e soltanto tu
 a decidere cos'è che devi fare.
E a decisão do que fazer com
o resultado acaba sendo sua.
Поэтому, как себя вести,
в конце концов должен решать ты сам.