Found using the google
Looks like the source is a person who worked with russias federal security service.
According to a leaked email from a whistleblower with Russia's Federal Security Service (FSB), months before Vladimir Putin began his disastrous invasion of Ukraine he was planning to attack Japan.
Dated on March 17th, 2022, the email was sent to exiled human rights activist Vladimir Osechkin from a Russian whistleblower dubbed “Winds of Change,” who has been writing regular dispatches to Osechkin since the war with Ukraine began
In the email to Osechkin, the FSB whistleblower stated that Russia was “quite seriously preparing for a localized military conflict with Japan.”
The whistleblower also mentioned the war in Ukraine and suggested that they were certain Russia would go to war, but that they weren’t sure why Ukraine was chosen.
“The whistleblower detailed movements of electronic warfare helicopters targeting Japan, while Russia's propaganda machine was also initiated, with a huge push to label Japanese as ‘Nazis’ and ‘fascists’.”
Christo Grozev, an expert on Russia’s Federal Security Service, stated that he believes the emails from Winds of Change are from a genuine agent connected to the FSB.
Grozev said he had shown the letter “to two actual (current or former) FSB contacts” and those agents had “no doubt it was written by a colleague.”
What advantage would Russia gain from attacking Japan? Well, the answer might have something to do with the two countries' dispute over the Kuril Islands.
Ultimately, however, the whistleblower wrote that the Russian leadership “sort of swapped out Japan for Ukraine.”
"But on the whole,” the FSB whistleblower continued, “war was inevitable for Russia due to the maniacal desire for war by the leadership…And now the bulk of the combat-ready units from that direction has been redeployed to Ukraine." So we shouldn’t expect a Russian attack on Japan anytime soon.
I saw lots of articles about this from back in november so its old news apparently and it appears that to a putin lover its just not credible that putin would ever consider such a thing anyways cause he is such a great guy and stable genius.