You mean how do you teach a language to foreign speakers if you don’t speak their language? It’s an interesting question with varied answers in terms of effectiveness, but for practical purposes in this discussion, the cheapo language schools in Japan really want their teachers to not use any Japanese in the classroom. They have you teach out of a series of textbooks and mostly don’t care about the outcomes for the students. In fact, the worse students do, the longer they stay applied to the courses that schools offer-- a relatively cynical view on things, but there’s a reason Japan ranks pretty low in English ability among Asian countries, despite being a wealthy nation. Like I mentioned above, there’s a reason you’re working for peanuts (and why the major language school companies don’t tend to want actual licensed teachers).
If you’re serious about wanting out, I’ll put links here to the major companies, but just keep in mind that they’ll pretty much provide you with a method of existing in Japan without being able to put away much savings, and like many large conglomerates they don’t really care about you if any problems come up-- there’s always the next weeb ready to take your place.
Ideally the best you can do is the JET Program, but that’s a long application process (about 6 months IIRC), and you’ll need to be under 40 (and from one of the listed native English speaking countries).
The rest I don’t have much direct experience with but the salaries are all less and they all sort of suck equally (Interac may be slightly better):
https://interacnetwork.com/
https://www.gabateachinginjapan.com/
https://recruiting.altmoot.com/
https://nova-holdings.jp/teachinjapan/
https://www.peppy-kids.com/
And there’s one that takes applicants to teach in universities, though you might need some credentials in ESL/EFL, but I haven’t checked very closely
https://www.westgatejapan.com/
If you have any questions let me know. I’ve been in Japan awhile, though I eventually managed to get a teaching license and masters, so I’ve been out of the ALT (assistant language teacher) game for over 10 years now.
