Well, admittedly it isn't common that a character is introduced that doesn't already speak a language the other characters naturally understand already.
There are plenty of actions and gestures that means entirely different things in different parts of the world,
that's why it's not that rare with issues and misunderstandings popping up during student exchanges and such when between certain countries.
@tunglam264 I work at a university with a rather international mix of students and staff. There is a primary school next to that university where my kids go to. Last time the principal talked about it, there was 51 different ethnicity in the student body at that school (it is kind of a record). Not all of them speak English when they arrive and the school has a special course for non native speaker. Most schools in New Zealand do.
Ok here is my hypothesis... That Rei is basically a god who know all things about humans that is there... as she is of humanoid form... I guess she was made for that purpose and then there is Reiji who can see her and that's why understand everything she says even if it is in another language.....
And is that chinese as the "Juju" seem to have that kind of attire.... why the hell doesn't she even learn english?? If she is from china I can understand it... and does the author really sees the other language like that?? Why isn't Reiji thinking about the loli goliath's origin now???
jesus thats some hardcore hand holding, already better than 99% of all current romance manga and more development with second girl than entire stories wauw