Koeda Yoshiyuki, a 51-year-old supporter, called Sanseito “the only party that can truly tackle the big problems Japan faces today”. Sanseito relied on social media, especially YouTube, to reach voters disheartened with politics-as-usual.

Its leader is a former supermarket manager who created his political party on YouTube in the depths of the coronavirus pandemic and campaigned on the Trumpian message “Japanese First.”

Japanese Premier Shigeru Ishiba vowed to remain in his post on Monday after his ruling coalition suffered a bruising defeat in upper house elections, prompting some in his own party to doubt his leadership as the opposition weighed a no-confidence motion.

The loss on Sunday left the Liberal Democrats a minority party in both houses of Parliament, while two new nationalist parties surged.

A bad night for the ruling coalition could cost the prime minister his job and make it harder to strike a deal with Washington before the August tariff deadline.

Japanese markets were closed for a holiday and global currency markets offered the only clear sign of a reaction. The yen , which had hit a three-month low of 149.18 per dollar last week, firmed to just under 147.7 after the results. That dragged the dollar (.DXY) down across the board.

The Japanese government said it is responding to "crimes and nuisances committed by some foreigners and inappropriate use of various systems."