I've actually worked on a Japanese company already and I'm looking for job on a couple others. I've done the test for CAPCOM and a few other companies so I know what they ask you for, and trust me, if you even slightly like the kind of mood you get on US game companies, you will probably not like what's going on in Japanese game companies.
First, as for what they ask for:
- Level 1 or 2 of JLPT (Japanese Language Proficiency Test) (I have Lvl 2)
- Being able to fluently express your ideas in Japanese, besides just having whatever JLPT level you have
- 9 to 5 job with "zangyou" (working extra time), sometimes up to until 10pm in many companies.
These are some of the things that I've seen in most companies. Now, there's another difference between many US companies and many Japanese companies, at least as far as I know.
In many US companies, when you try to look for a job, you say you can do textures, or models, or concept art, or level design, etc.. In many Japanese companies you have to be able to draw pretty well besides doing 3D, even if you are never ever going to draw a single sketch in your job.
Other than this, you will have to stay with lots of incredibly ridiculous people that are stuck in the 90's and early 00's when Japan was the leader in the game industry and think of foreigners as people that "don't get it" (seriously, I've met a few of those even in my current school, and it's.. sad). But then again there's people like this everywhere, so whatever.
But if you ask me, right now there aren't all that many reasons to look for jobs in the Japanese gaming industry, unless you enjoy challenging yourself.
Ah, also, Japan has this weird thing where they do all the recruiting thing during the months of March up to September (with most ending in June/July, actually), so if you don't apply during that time, you will have to wait a year.
There are some companies like Grasshopper that don't work like this, though. But that company doesn't pay very well either, so I would not suggest it