Do both countries have a particluar hot spot that existed in the past, and if so, does it still exist now? Have their wars historically been bloody or transient, and are they now considered "friends"?
Rather than saying they had X number of wars, it would probably be more accurate to say that the two countries had a continuous ongoing conflict from 1895 until 1947, with occassional brief breaks for recuperation and retooling. In fact, the territorial disputes didn't even really end there, but the fighting did due to the Cold War.
Since then I think just about all the disputes have been resolved, save for the status of four small islands near Sakhalin.
Russia and Japan had one war, and several smaller scale conflicts, in the 50 years between 1895-1945. They are NOT natural enemies.
Their emnity arose out of the power vacuum created by the collapse of China in the lat 19th, early 20th century. This caused them to both covet Manchuria, for two different reasons.
Russia wanted a warm water port on the Pacific. Port Arthur (in Manchuria, leased from China) served the purpose. Vladivostok (ice-bound for four months of the year), did not. Japan wanted the Manchurian INLAND for its natural resources and living space. That was the cause of the 1904-05 war.
China has since "woken up" and re-asserted her claim to Manchuria, thereby removing the main source of emnity between Russia and Japan.
It is noteworthy that although there were two "border incidents" before World War II, Russia and Japan had, and observed a non-aggression pact for most of the war (until Germany was defeated). Essentially, they both had "other fish to fry."