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?
Supposedly, they learn it 
in the early grades.
Das lernt man schon sehr früh,
hat Eri-san gesagt.
Eri decía que se lo enseñan pronto.
Eri decía que se lo enseñan pronto.
Eri m’a dit qu’ils l’apprenaient
dès l’entrée en primaire.
Pare lo insegnino ai primi anni.
Dizem que é ensinado
logo nos primeiros anos.
Ещё в начальных классах
про них рассказывают.