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.
In other words, I was born
 thirty minutes earlier.
.بعبارة أخرى، أنا أكبُرك بنصف ساعة
Ich bin ganze 30 Minuten früher geboren.
Es decir, que yo nací
media hora antes que tú.
Es decir, que yo nací
media hora antes que tú.
Je suis venue au monde
trente minutes plus tôt.
Quindi sono nata mezz'ora prima di te.
Ou seja, eu nasci 30 minutos antes.
То есть я родилась
на 30 минут раньше.