Seems like Onoda's situation is that she was born in the United States to a white American father and a Japanese mother, and the father abandoned the family and the mother moved back to Japan when Onoda was extremely young. So she has almost entirely grown up in Japan but technically had US citizenship because of US birthright citizenship laws until she deliberately gave it up; and of course is visibly half-white. It wouldn't surprise me if part of her personal anti-immigration stance was grounded in anger and sadness about her non-Japanese father abandoning her and her mom.