What to do with my disposable income

So every month after everything is settled, I find myself with anywhere between 100k to 200k left, just being transferred to my bank account. I want to make better use of that money, so any suggestion is appreciated.

Here's my situation:

1) already contribute the maximum to the Nisa tsumitate. Maybe I should look into Nisa seicho?

2) I already have 6 months worth of salary in savings. Maybe increase that to 1 year?

3) Something like Nisa where I just set it and forget it is perfect for me.

4) I'm not Japanese and in my early 30s. Don't know if I'll stay in Japan forever.

by Anonymous-Songmaker