There is a low-cost SIM in Japan called "povo". The lowest price is 220 yen for six months.
The internet is very slow and calls are also charged separately, but it is cheap. You can receive calls and make calls on LINE and so on.
I switched to this company because it is very economical.
With the introduction campaign, I can use unlimited communication today + 3GB from tomorrow.
I would like to try it for a while.