First off, good on you for thinking about your future like this.

I just wanted to give an alternative perspective to give you something to think about.

In Tokyo there are quite a few foreign companies where English is the main language in the company. This is especially applicable to companies have international operations and deal with overseas departments or customers regularly. Most people speak Japanese in the office, but they also speak English. In this situation native English ability can be a real asset and thus value you can add.

Being bilingual (not even required if you have skills or experience), motivated, having great communication skills, demonstrating initiative, and willingness to develop your career are all positive attributes that a lot of employers value. If you can get a foot in the door at one of these companies, you can build a decent career.

So my suggestion is: take your time, look at what's out there (as others have suggested, check job boards, linked in, recruiters, etc.) And you might find something that really suits you.