I was also an asian studies major and a linguistics major. You have a few options:
-Teaching English (if nothing else than helping you get your foot in the door)
-Becoming a translator/interpreter (This is what I do, it will take a bit more than 4 years of university Japanese but you will be on your way)
-Quite a few other options (see below)
Really the question you need to ask yourself is, what do you want to do with your Japanese? You can do anything with your Japanese, limited only by your proficiency, because most people just view language as a medium through which to do other things. Does academia interest you? (being a professor and teaching Japanese history, language, etc.) Or maybe Business? What I'm saying is language in itself is very vague, with infinite possibilities, so you'll have to narrow your interests down, and work from there.
Not a lot of people who graduate with a degree like Japanese go straight into a job. Have you considered the
JET program? Or a postgrad advanced language center like
Inter-University Center? Quite a lot of liberal arts majors opt for graduate school as well, both to ride out the bad economy and because competition for jobs can be harsh for liberal arts majors without an advanced degree. So never eat dinner alone! Make connections..