[GoNative]

Just trying to give people a realistis idea of what it's like to try and work in Japan. If you're wanting a job in a career related to what you are studying in your home country (outside of the english teaching sphere) then you'll struggle to get a job with a Japanese company unless you have business level Japanese or a specialist skill not commonly found in Japan. To secure a sponsored work visa for you a Japanese company will have to be reasonably convincing that a Japanese national can't be found who could do the job just as well. They have to justify hiring a foreigner.
That's not to say you can't get a job here. You'll just probably end up working for a foreign owned company that has branches in Japan. As MMM points out most positions if you don't already have a working visa will need to be applied for from your home country. You can do what I did and use an english teaching job just as a stepping stone to get the visa and then move on to things you'd prefer to do.