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?
What concerned us in this case was 
a different, more complicated problem.
Worum wir uns gesorgt haben,
war ein anderes, komplizierteres Problem.
Lo que nos preocupaba
era un problema más complicado.
Lo que nos preocupaba
era un problema más complicado.
Ce qui nous préoccupait
était une chose bien plus complexe.
Ma le nostre preoccupazioni
 erano un po' più complicate.
O que nos deixava apreensivos
Нас, учёных, волновала
проблема несколько иного рода…