Frankly it'd be easy to earn enough to live on just by doing shitty part-time work. Obviously that isn't something to aim for, but don't fuss too much about jobs. As a Westerner (and especially as one who appears competent in English), you've always got language teaching open to you.
The biggest obstacle I can foresee is that you will need a visa to work before you actually come to the country. But for most positions, a company will be reluctant to sponsor some random guy they've never dealt with. One possibility, which would be helped by studying Japanese culture and language, is going over as an exchange student and using that as an opportunity to network, set up an internship, or even get a job (after being granted a right on your student visa, which is easy once in Japan). The former two provide you a way to come back working, and the latter provides you a way to get a working visa early-on which would allow you to look for a more appropriate job while still in the country.
>>1925This really depends on the company. More and more places seem to be providing more and more holidays, especially in the sorts of sectors where foreigners are likely to be hired. Of course, 休まず送れず働かず hardly guarantees an unpleasant experience even if you are at an old-fashioned company.