Here’s one option- build a carrier on G1. Build a transport on both G2 and G3. Stack in E Europe as much as possible. When you are able to gain numerical superiority, move your E Europe stack to Karelia along with 6 infantry from Germany/ W Europe. You can now hold the north of the board, and you control and/ or threaten Norway/ Karelia/ Archangel and threaten the Red Army in W Russia. Until the US or Britain brings a credible threat to your Baltic fleet, you can continually reclaim Norway if the Allies are landing there. If Norway becomes an Allied meat grinder then Russia is being asked to deal with Japan by itself, which is a tall order when an Allied KGF strat and logistically competent Japanese play are combined.
This is just one of many paths; it has been employed against me with success and I have used it with success.
The key to this move is that it dictates the pace of the game to the Allies until they are able to overcome the Baltic fleet. By that point the Japanese are seriously eating into the backside of Russia, and reinforcements from the UK and US have been chewed up perpetually in the German northern meat grinder. The idea isn’t for Germany to become a massive force, but for it to take the brunt of the war and chew up units while Japan builds the forces necessary to topple Moscow.
Expect to eventually lose the Kriegsmarine and go into full turtle mode with Germany. If you’ve been playing Japan well you’ll have a legitimate shot at killing the Russian Bear.