It is probably relevant to your understanding of this matter that the Japanese equivalent of payday lenders, which are owned by banks roughly similar to CitiBank, have in the past outsourced collections to the yakuza as a matter of policy.

By law and custom the United States has a lot of protections for debtors. Japan... well...

Ah, so she borrowed from a bank and the yakuza came knocking? Yes, if that is the case, that is a different matter.

I think regardless of who you borrowed money from, collection by death threat should probably be illegal.

If you allow collection by death threat as a legal way to still give money, the Yakuza will just collect money that way always.

There must be a way to stop it all. However the law does indicate that ANY involvement with them will screw the business, so banks using the Yakuza to collect will now be equally liable.

it could also be racket, which is still prevalent I believe. At least several foreign bar owners told me they had to give money to them.