I find the Idea of the Axis winning WWII and the Japanese managing to occupy the west coast of the US to be pretty silly. Although the IJN was quite an effective fighting force, as far as a land war the IJA would probably have been clobbered once landing in the US, not to mention that the Axis powers combined did not have the manpower to successfully occupy all of the territory of the Allied powers.
Yes the IJN was quite capable. Even formidable. I'll even say circa-1941 a division of Japanesse Infantry would beat a division of US infantry.
The simple problem is logisitics. It's a heck of a long way from Tokyo to LA. Supplying an invading force, to say nothing of actually getting the job done, would be an impossibility for the Japanesse.
The most plausable scenario I can imagine would be them getting all of the US's Pacific holdings including Alaska. That's along with a simotanious German victory.