[Nyororin]

From what I have heard, the money doesn't have to stay in the account. Basically, they just want proof that you have access to enough money to support yourself while in Japan.
It seems to be pretty common to borrow the money, show proof of it being in your account, and then return the money to whoever you borrowed it from... Or just show the account of family with enough.

As it really is just to prove that the money is there and can be accessed by you in the case of an emergency, I wouldn't consider it a last resort to ask family. It isn't as if you are going to spend the money - just show that it exists if you need it for some unforeseen reason.