When I originally came to Japan I wasn't a teacher. I worked for a company that sold guitar pedals and I was a permanent employee. I didn't realize how big of a deal that was until I decided to quit that job. I interviewed for other jobs and a few of the companies that I interviewed with asked me if I was a permanent employee and were surprised I was willing to quit with the type of job that I had. Many people can become permanent employees if they are Japanese but the number of foreigners who get offered permanent positions in Japan is quite rare.
If you look at most teacher job listings on major websites they will list the pay for the year but any mention of increasing pay the next year is absent compared to any job that would have you be a permanent employee. This would essentially mean even if you wanted to work as a teacher for years in Japan the chance of you getting an sort of pay increase is silm to none. Of course there are exceptions to this but only if you have master's degrees or advanced certifications for teaching abroad.
When I first wanted to move to Japan I didn't really know what I wanted to do here but I just wanted to get better at the language and improve my Japanese language ability. So getting a master's degree or a TESOL certification didn't seem that important. Now that I have been teaching for a few years I realize that there really are lots of benefits to doing that if you really want to stay in Japan long term for teaching.
I have a acquaintance who teaches at a local university and the reason that he is able to teach at the university level is simply because he has a master's degree. His master's degree has nothing to do with teaching however simply the fact that he has graduated from that level of education gives him opportunities that I do not. I find that to be quite illogical. One of the people that I currently work with has been living in Japan for 10 years and has been teaching the entire time he has been there and he is extremely good at it. However the fact that he doesn't have a master's degree means that he is stuck teaching at a lower level education with a set salary with no chance of getting higher.
In Japan you can only offer someone a yearly contract for 5 years in a row. After the 5th year you have to either give the employee a permanent contract or fire them. Even if the employee is great some Japanese companies will decide to let that person go because they don't want to have the burden of a full time foreign employee. It's sad but true.
There doesn't seem to be much happening to change this either. I am currently working as a direct hire ALT in Iwate Japan and even though I work the same hours and the same days as a Japanese teacher or public official my salary and contract are completely different. I have only been here one year but the other ALTs who I am working with have been receiving the same salary for years now and that it extremely unsettling. When I ask myself why are we treated differently the only reason I can come up with is the fact that we are not Japanese. I have had thoughts creating a national union for English teachers in this country and frankly I think there should be something like that. I am at the good end of the spectrum too. Most ALTs make less than me and have a salary the fluctuates depending on the number of days they have off a month. I have a steady salary every month of the year.
If Japan really wants to have better English education there should be laws or regulations in place that make sure that people that want to help with the education here get treated equally. I think many people are just happy to get their foot into the door when they start working in Japan but after a few years you really just want equal treatment.