https://en.wikipedia.org/wiki/Shikotan

https://en.wikipedia.org/wiki/Kuril_Islands_dispute

In the event of controversy I will let a council of mods decide.

I think if Japan gains de facto control of the island for less than a week and it's obvious that it's going back to Russia later then that doesn't count. But if it's longer than that, then it does. I don't know how I would resolve if Japan gains control of the island for what seems like an indefinite period of time but ends up only lasting six days. I guess I would resolve to 50%. Hopefully there won't be a difficult edge case like that.