Not really. Southern Kuril islands were negotiated by USSR with USA and UK as a price for USSR joining the war against Japan during WW2 after Germany was defeated. But after WW2 occupied Japan under the pressure of USA refused to sign a peace treaty with USSR and regulate territorial dispute. Russia and Japan were in talks about peaceful resolving Southern Kuril issues for decades, but the main obstacle is that Japan is still an occupied nation with USA military bases stationed there.

After USA pressured Japan to sanction Russia and send military support to Ukraine, all talks about Kurils were terminated.

No? They've expressed zero interest in resolving the disagreement via force, and parts of Ukraine are currently held by Russia in a similar fashion.

Then what was the point of your example?

What does Japan gain from the idea that one country cannot take another country's territory by force, if it is in fact Russia that is in control of these islands?

If anything, Japan would like them back eventually. All attempts at diplomacy have failed, so force would be the only other option.

> Then what was the point of your example?

That Japan most certainly doesn't want territorial disputes to be resolved by might and current possession status.

> If anything, Japan would like them back eventually.

Yes, and they'd prefer "Russia currently holds them, so they get to keep them" not to be precedent. Russia is attempting to set that precedent in eastern Ukraine, Georgia, and Moldova currently.

So Japan can get a win out of the Crimea situation either way?

If Russia „wins“ they could justify using force to free their „historic“ possession.

And if Russia „looses“ they can argue having military control does not imply ownership. And that usage of force to revert military occupation is legal.

Any diplomat that can't spin both a spin and a loss is not a very effective diplomat. That said, "Russia shouldn't be able to force resolutions to territorial conflicts with military might or mere possession" is consistent across both scenarios.