Can you self-sponsor from home?

I want to move back to Japan after several years away and I've been offered a part-time only teaching job by my old employer. Does anyone know if I can self-sponsor to get a wokring visa in this situation? Where could I find more info - my local consulate was very unhelpful.

No, I am afraid, there is no work visa for the self employed.

Thanks for your reply, but I wouldn't be self-employed, my previous empoyer has offered me a part-time job.

Still you will need an employer to be your "visa sponsor." (The meaning of "visa sponsorship" is different from sponsoring in the sense of providing for a living.) And offering a part-time job is not enough as a sposor - your previous employer will need to employ you, with appropriate salary, with appropriate papers, and apply for your visa on your behalf, so that you can work for him.

So it is possible to self-sponsor when you are already living in Japan, for example, when you want to renew a wokring visa - but it is not possible if you want to organise a working visa from your own country? What do freelancers do then?

When you want to have your visa renewed (or when your employer wants to renew your visa so that you can continue to work for them) the same procedure applies - the employer provides documents, etc.

Freelancers have other visa status granted - for example, so-called spouse visa (married to a Japanese national), or already on permanent resident status (prior to applying for this, you'd have been on employer-sponsored work-permitting visa for 10 years, or for 5 years if married to a Japanese national).