Saving money as a beginner

I'm have been in Japan on a working visa for about six months now and intend to stay in the country for another 4 years or so. I have a steady job and am looking to find a way to save money past just leaving money in my bank account. I looked into if theres anything like a high yeild savings account in Japan, but it doesn't seem like that's a great option with the rates of the accounts. I'm originally from America and still have bank accounts there. Should I just move money from my Japanese account into my American accounts? I read a bit about NISA, is that something worth looking into? Any advice is appreciated!