I recall in history class learning that the Japanese could have attacked the USSR in the 1940s and potentially split Stalin's forces - which presumably would have been more useful for the Nazis than bringing the US into the war.

Which would indicate that Japan wasn't part of the Axis in any real way.

At the same time, after Pearl Harbour, the Nazis declared war on the US (siding with the Japanese), indicating a close relationship.

But again, I cannot imagine the Japanese fitting into the Aryan image if the Russians didn't...

So, did the Nazis have a relationship with Imperial Japan? If not, why are they always referred to as the Axis?