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.
Hold on a sec. It looks like I'm 
trying to seduce him, doesn't it?!
!مهلاً لحظة. يبدو وكأنّني أحاول إغراءه، صحيح؟
Augenblick mal.
Espera… No parecerá que estoy
intentando seducirlo, ¿o sí?
Espera… No parecerá que estoy
intentando seducirlo, ¿no?
Maintenant que j’y pense…
Fermi tutti.
Sembra che stia cercando di sedurlo, vero?!
Espere um pouco. Assim parece
que estou tentando seduzi-lo!
Погодите. Со стороны кажется,
будто я пытаюсь его соблазнить?!