In reality though they never declared war the japanese did fight in Russia in large numbers in 1939. The fighting culminated in the battle of Khalkin-Gol, during which the japanese 6th army was decisively defeated. This prompted the japanese to put off an invasion of the USSR until after the war in the pacific was over.

Therefore to say that Japan didn't try to invade Russia is a little misleading. They may have not declared war, but there were definitely large scale operations on the border.

Source: "Stalin's General" by Geoffrey Roberts

Funnily enough, Japan had actually invaded and occupied Russia before World War II. I refer to of course the Siberian intervention during the Russian Civil War. Japanese troops backed Admiral Kolchak's regime in the Russian Far East, withdrawing only due to strong diplomatic pressure from the US and the UK who were concerned that the presence of Japanese troops was more to support Japanese imperialism in Russia rather than as a force to suppress the Communist threat.

There were no plans for an invasion or occupation of Russia. Japanese military planning against the Soviet Union was almost entirely on a defensive footing. The main strategic concern of Japan was that the Soviets could potentially invade Korea (a Japanese colony) as well as sever the Manchurian railroads that were Japan's lifeline to its forces in North China. The Soviets had intervened in China on several occasions, and Japan was concerned that the Soviets might take a more active role in inhibiting Japan's invasion. Large military exercises were routinely held by the Kwantung Army-the Japanese army group responsible for the defense and administration of Manchuria-and a fixed defense line in the north was constructed to help repel a Soviet attack. The key objectives Japan was concerned about were the railways that stretched through Manchuria and connected to Russia, Korea, and China, especially the South Manchuria railway. The Korea Army, the army group responsible for the defense of Korea, was responsible for defending the Soviet-Korean border, which was constantly disputed due to vague claims by both sides and led to skirmishing as well.

The skirmishing finally came to an end with the Soviet-Japanese non-aggression pact signed in 1941, which was partly caused by Germany looking to repair its relationship with Japan after the Molotov-Ribbentrop pact (which had outraged Japan as it seemed to be in contravention of the Anti-Comintern pact that Japan had signed with Germany before, to say nothing of German aid to Nationalist China previously). The agreement was widely considered to be have been one of convenience, and although the Japanese considered breaking it after the initial success of Operation Barbarossa it was decided that Japan's resources between the war in China and preparations for the Pacific War were already too outstretched to even consider the idea. For their part, the Soviets abrogated the pact in 1945... but that's another story.

Just to be clear, are you saying that Japan considered invading Russia instead of Manchuria circa 1931?

People are bringing up the battle of Khalkhin-Gol, which didn't happen until 1939, shortly after the Sino-Japanese war began in 1937.