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.
If you act like that at school,
،إن تصرّفتِ كذلك في المدرسة
Wenn du so was vor all den Leuten machst,
geht dein Ruf doch den Bach runter.
Si haces cosas así delante de todos,
vas a arruinar tu propia imagen.
Si haces cosas así ante todos,
te vas a cargar tu propia imagen.
Avec ce que t’as fait,
ta popularité va en prendre un coup.
Se ti comporti così a scuola,
Agindo assim na frente de todos,
Если будешь
при людях так делать,