Sometimes when otherworldly creatures come to Earth, I can't help but wonder how they know perfect japanese. Especially when they come by accident. In Jahy-Sama, the demons don't plan to go to Japan, they just end up there because the underworld is destroyed. Jahy makes it clear she's fairly oblivious to the human world, so it's a surprise she ends up in Japan and speaks perfect Japanese.

On the other hand in Raphiel Dropout, it's shown that the kids go to school and traveling to Earth is part of their curriculum. It would be retarded to not have learned Japanese beforehand.

I think there should be one where the cute girl gets to Japan and doesn't know any Japanese. And learning along the way is part of the arc. Bonus points if she's an entitled brat who gets really angry about the situation constantly. Maybe there could be a nerdy sidekick character who can do translations, but she isn't around 24/7.