The relationship between Russia and Japan isn't very good due to territorial disputes over the Northern Territories and historical issues, leading to ongoing tension between the two countries.
However, for Chen Yu, these matters are of no real concern.
What do the land issues between Russia and Japan have to do with him, a Chinese?
While Japan is currently under his protection, this doesn't mean Chen Yu is obligated to solve Japan's territorial issues.
The protection of a demigod is merely a shield against severe dangers emerging from the Supernatural World, rather than a justification for the Japanese government to act recklessly under his banner.
This time Chen Yu accepted an invitation from Russia's Great Emperor to go to Russia, both to fulfill his promise to the Russian government to help them summon a ship-girl, and to inspect the yacht that the Russians built for him.
