i have lived and worked in japan for about 8 years in total. during that time i have worked as a swimming coach, okonomiyaki cook, english teacher, sake yasan dilivery man, and marketing manager for a university. i think there are lots of things to do, but it depends on your bf's visa. if he's on a working holiday he can do almost anything except working in pachinko or snack bars (that's the law, but in reality you can). if he's coming on a work visa the options are much more limited. usually gaijin can only do jobs that japanese people cant do. eg teach english, translation, or work for international companies that need native speakers.
if he wants to ask me about it directly please send me a message and i will give you my email.