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.
How much longer do you plan on calling 
me by my given name like it's nothing?
إلى متى ستواصل مناداتي يومي-سان بلا اعتبار؟
Dass du mich immer
„Yume-san“ nennst.
¿Piensas seguir llamándome
por mi nombre como si nada?
¿Piensas seguir llamándome
por mi nombre como si nada?
J’en ai marre que tu m’appelles
par mon prénom.
Per quanto andrai avanti
a chiamarmi per nome come se niente fosse?
Por quanto tempo ainda vai me chamar pelo
meu primeiro nome como se fôssemos próximos?
Долго ты ещё будешь как ни в чём не бывало
обращаться ко мне по имени?