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.
For that bookstore 
on Karasuma Street, by chance?
إلى متجر الكتب في شارع كاراسوما، صحيح؟
¿Van a esa librería
de la calle Karasuma?
¿Vais a esa librería
de la calle Karasuma?
Per caso state andando
nella libreria di Karasuma-dori?
Por acaso vão até aquela
livraria na avenida Karasuma?
Неужели хотите сходить
в книжный на улице Карасума?