There was someone on JF that is doing just that, and they posted on here a while back. The thread is something about his salary for finance or something. But I would have to say, keep an eye on the job section of
Jobs in Japan: Jobs - Japan Jobs - Japan News - Japan Info - Japan Apartments - Japan Classifieds - Japan Forums because not all the finance jobs you could get will not require a high level of Japanese. Also if you are really serious about living here for an extended period of time, you could come over and "suffer" through a year of teaching English while you learn the language and seek other jobs.