@user5924704
No , where and how you received the award is not material. That is since the award was issued by a US entity while you were in the US as NRA, it is still US sourced income and therefore generally taxable income to US.
What was the reason for the award ? Consultation fee. speaker's fee , help with travel expenses or what ? How long were you in the US with ESTA ( visitor visa ) ? What were you doing ?
Absent any contravening facts, I am still of the view that you need to file a 1040-NR recognizing the income, pay the US taxes and then in Japan recognize the income as part of your world income and request Foreign Tax Credit ( against Japan tax ) per Japan-US tax treaty article " double taxation relief".
Is there more I can do for you ?
