Mizuto and Yume used to date, but now they've suddenly become stepsiblings. Both of them agree that they don't want to do anything that'd disappoint their newly remarried parents. However, neither of them can accept the other as being the eldest sibling in the relationship. So they both agree to settle the matter with a game. Whoever does something in conflict with what people might consider normal sibling behavior, loses. Making them the younger sibling.
We're walking to school separately 
starting tomorrow, got it?
سنأتي إلى المدرسة بشكل منفصل
بدءًا من الغد، مفهوم؟
Ab morgen gehen wir
getrennt zur Schule.
Vendremos por separado desde mañana.
No volveremos a venir juntos, ¿vale?
On viendra séparément,
à partir de demain.
Da domani verremo a scuola
ognuno per conto proprio, capito?
A partir de amanhã viremos
separados, entendeu?
С завтрашнего дня
ходим в школу отдельно, да?