denied entry (airport to airport)

Your sister takes care of an elderly, doing household work and that already constitute an employment status whether it is paid or unpaid. The relationship between the aunt and your sister is not an issue and won't receive special consideration. By no means your sister is a visitor anymore

Helping around isn't illegal, and I guess you have a broad interpretation of what it means to be employed.

So someone who is on a dependent visa helping out their spouse would constitute "employment" under that broad definition as well? I don't think so.

In fact there's a broad definition of what you can do and can't do as a Temporary Visitor.

For example it is LEGAL to come over to Japan and sign a multi billion dollar contract with a Japanese company under Temporary Visitor status.

The fact is Temporary Visitor means just that, Temporary Visitor, if you are coming and going then it becomes suspicious, because you are no longer a "temporary visitor". So the Immigration Officer can deny you entry for any reason.

To Cherry23,

"my sister already stays in japan for six months with a tourist visa after two months she go back to japan but immigration inspector did not allow her to enter japan."

So it is crystal clear that your sister was not on dependent status. I believe your sister had provided all the evidence, including the family registration as you claimed, to the immigration officer for consideration and still, she was denied entry. It showed whatever evidence or reasons she put up were not good enough to clear the officer's doubt.

As suggested by some other posters, it is best for your sister to approach the Japanese embassy for the correct answer. If she can provide fresh documents which merit compassionate grounds, surely the embassy will consider the case. You are not in a dead end yet.

Thank you so much for your answers...Thanks to all your informations...
God bless to all and more power...