It's borderline if you live by yourself in the city, especially if they don't cover travel expenses. There's a chance your health insurance and pension will be deducted from that too, assuming they cover it.

If you're working for a Japanese company, you'll probably be working a lot more hours, and taking a lot less holidays than you would be in the US or UK. 4x is a low estimate for the actual amount of work you'll be doing.