Just about any job which requires you to go to Japan will take you to Japan. It's a bit of an open question
You could work the diplomatic corps. You get sent where you're needed, but that
might turn out to be Japan, especially if you already speak the language before you apply.
You could work for a company with offices in Japan and request a transfer when a Japanese vacancy opens up. Again, some language ability may help, dependent on the role's requirements.
Can you get hired as a Manga writer when you're previously-unpublished and don't speak Japanese? Maybe. TokyoPop run an annual competition in the US to find new Manga writers and artists, but your best bet is to team up with a good artist before you apply. Manga
writers are ten a penny. Either get good at drawing, or team up with someone who's already there but who sucks at the writing. And speaking from experience, let me assure you of this: For every good writer out there, there are 999 bloody awful ones. Your best chance of getting published is to be that one in a thousand who doesn't suck.
If you are genuinely serious about kick-starting a career in writing comics, then start it. Make your world, write your script, get it drawn, and launch a webcomic and upload 1-8 new pages per week. Grow a following organically. If your product is good, word of mouth will be the only advertisement you need. It will take time to build a readership and gain recognition, but it shows passion, and you can work on multiple projects at once (time pending, of course).