Well that was a sarcastic joke at the end. The US has not made any threats to Japan since after the bombing. The other countries listed are a different story though.

Russia: I think you have forgotten that the Kuril Islands are still contested territory between Japan and Russia. Russia's same policy is there that they will retaliate if their territories are "attacked." The exact same line with Ukraine. Putin has suggested he would take out Japan and (South) Korea quickly as they are the US's main launching points of an attack. Getting them out of the war quickly gives Russia a serious advantage and the US a serious disadvantage. This is ongoing and has been in discussion since the Cold War. Policies have not shifted on this. Russia has actively been violating international nuclear armament treaties and this has been big news since 2014. So, current.

China: Has been much more explicit and aggressive, stating that they will nuke Japan until they unconditionally surrender if they even send a single troop to defend Taiwan[1]. This video is 2021. They have also made similar threats to Australia after a deal with the US for nuclear powered subs (which would not have nuclear weapons) saying that any nuclear nation is not immune from nuclear attack.

North Korea: idk, last week when they launched their test missile directly over Japan?

I get that searching with respect to Russia might be difficult right now because everything is focused on Ukraine and Google overfits search results. But this has been in military discussion for decades. Maybe it is just saber rattling, but these are still things that have been said.

[1] https://twitter.com/jenniferzeng97/status/141497128516000563...