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?
Except, if you expand 
the previous concepts...
Pero desarrollando lo que ya vimos…
Pero desarrollando
lo que ya hemos visto…
Si tu t’aides de ce qu’on a appris
jusqu’à présent…
Se però la risolvi così,
 procedendo come sappiamo fare...
Mas considerando o que eu fiz até agora...
Но если исходить из того,
что мы изучили до сих пор…