[jaysoncena]

I'm not sure how easy it is in Japan but in Singapore, It just took me 10-15 mins to file my tax. 1. Login to IRAS(tax bureau) portal using the national ID (for me as foreigner, I used my employment pass ID) 2. Open the page for filing income tax 3. I entered total annual salary and allowances 4. I have donated to a government-recognized charity and this is automatically reflected on the form. It seems that the charity uploads donation infos to IRAS 5. Check if the tax relief for having a child is there 6. Click submit 7. Review and re-submit

You also have an option to do installment, deducting from your bank account monthly.

I don't have any other source of income so it will be different for other people.