Just left Japan and having spend a few years there, not much you can do to reduce income tax. Normally if you have a house, or a child you can have some deduction. Buying insurance or also proof that currently you are supporting your parents is also tax deductible. How to show proof you have to ask around....

Really depends on your lifestyle. I have  family and able to survive and save some $$ as well. I am sure you friend can withdraw the EPF(about two months of last drawn salary) and also the retirement scheme that the company bought for her/him.

That is low for a senior executive. Basically that is the salary of a fresh grad.

Very low. Thats fresh grad, senior would get double of that easily. How old is she?

Thats still low. I hired a Malaysian from KL who cant speak Japanese and I pay more than that, which also include some housing allowance.