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.
Now then, since this is the first round, 
let's keep it simple.
،والآن، بما أنّ هذه هي الجولة الأولى
سنُبقي الأمور بسيطة
So. Weil’s das erste Mal ist,
halte ich’s ganz einfach.
Muy bien, como es la primera,
será algo sencillo.
Muy bien, como es la primera,
será algo sencillo.
Bon, pour ton premier gage,
je vais faire simple.
Allora, visto che è il primo round,
facciamo una cosa semplice.
Agora, já que esta é a primeira
rodada, vamos simplificar.
Итак.