Income tax refund after leaving Japan

Hi,

I finally got my pension refunded, so now it's time for the even lengthier process of getting my tax refunded. It seemed like a pretty basic bit of bureacracy, I found the appropriate form, however according to my boyfriend's accountant friend, I need to get my former company to fill in some of the info. The issue here is that I worked for 4 different companies, one after the other.

Could anyone advise what to do? As usual, the official website doesn't exactly provide a wealth of information, so any help would be much appreciated.

Thanks!