Ukraine has a proper army and the support of Europe, albeit with dated weapons. Japan has neither and it's dubious whether the United States would step in. Hokkaido has always been under threat from Russia and the Soviets quickly took the Kuril Islands, which wasn't even originally theirs.
No. The only way the Russians could prevail is to break out the nukes, and that would always run the risk of a nuclear response from the US. Japan's navy is more powerful than the Russian pacific fleet in a conventional conflict. Any attempt to land on Hokkaido would be stillborn.
Even if they managed to land they would probably be pushed off pretty quickly. Japan's military is more powerful than that of Ukraine, and the Russians are already having trouble supporting troops just across the border. There's no way they would be able to support an invasion force over water. I'm skeptical the Russians could pull that off without opposition, something they would certainly have in spades.
The Russians lost control of the Black Sea to a country that doesn’t have a navy. Its naval incompetence is legendary. There is zero chance of them conducting an amphibious invasion against anyone any time this century.
If the Okinawan Americans aren't going to do something useful for Japan, Japan would be very happy to kick them out and stop them harassing the locals.
A land invasion of mainland Japan is so unrealistic that even the US in WW2 didn't attempt it.
Japan is a turn key nuclear state, that is all…
The United States defends Japan. The United States has nuclear weapons.
Knowing those two facts, we can conclude that Russia will not be invading Japan as long as it is protected by the United States. The calculus is very simple when nuclear weapons are involved.
Also, keep in mind that D-Day was the largest amphibious assault in history and all they had to do was cross the English Channel. Russia invading Hokkaido would be suicide, the US nuked Japan rather than try invading the homeland to end WW2 and we controlled every island surrounding Japan at the time.
> Japan has neither and it's dubious whether the United States would step in.
There is NO QUESTION the US would provide a full defense of Japan against any aggressive party.
The US has multiple military bases in Japan, with 35,000+ military personnel. Japan pays the US billions every year to support the US military presence there. Japan is also a too-big-to-fail economy (4th in the world) and US trading partner. And strategically, what do you think the US "pivot to Asia" means, if not defending close US allies in the Asia-Pacific from unprovoked aggression?