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.
Looks like Mom and Mineaki-san 
will be home late tonight.
يبدو أنّ أمّي والعمّ مينياكي 
.سيتأخران في العودة اللّيلة
Mama und Mineaki-san
kommen heute wohl spät nach Hause.
Parece que mi madre y Mineaki
llegarán tarde hoy.
Parece que mi madre y Mineaki
llegarán tarde hoy.
Nos parents vont rentrer plus tard,
aujourd’hui.
Pare che la mamma e Mineaki-san 
stasera torneranno a casa tardi.
Parece que minha mãe e o
Mineaki-san vão chegar tarde.
Похоже, мама и дядя Минэаки сегодня
придут поздно.