Dear Ms. Hau
Hello.
The 40,000 yen are income tax withholding.
Income tax withholding is a tax to payment.
The tax will be paid for a Vietnamese government, not Japanese.
40,000 yen every month of company usually keeps it from January to December.
When 1 year ends, the, kept money is sent to RKH from Japan.
When there is other payment, it may be offset.
Thank you.