Nice clean layout, and it seems they are also selling photos.
We're probably losing a lot of opportunities by sticking to American and European agencies only but...
we could even manage to find out where's the signup button but what if they require keywording in Japanese?
They don't require keyworing in Japanese. They are translating the keywords for you.
The only thing is that you'll have to send the signed agreement to them by post, so it will take a while.
After that, you'll have to wait also for the review process, maybe a month or two.
In my case, they said it will be a month or two.

Good luck