Working holiday visa for a dual national: residence requirement?

Asking for a friend who isn’t on reddit:

He is a Dual National of the US and the Netherlands, but lives in the US and has lived in Japan for half a year in the past on a student visa issued to him in his US passport. Now, he wants to come back to Japan on a WHV using the Dutch passport. Now he found out he has to live in the Netherlands to be eligible to apply, but the question is, how does the Japanese embassy see residence? Does he simply have to provide a dutch address, a resident registry entry from the town hall, or something like that? And also, is it a problem that he was in Japan before with his US passport?

by Yonda_00