I would advise you not to be (over)confident about your's numerous air bases at HI. Allies will recive B29 soon, if they didnt already, and they can shut down your AFs. It will be much more difficult task than it was in Solomons, but with this current air model, "the bombers will always get trough" it is certainly doable. And he has many choices, he can put pressure on closer bases (within his fighter radius) and suddently attack your rear AFs which will be weaker defended (just one example)...
You dont have many options, except massing base forces and construction units at Home islands. I would pull out all BFs from the frontline (Burma, southern DEI, New Britain...) and move them to Home islands (anyway, Allies can shut down all your AFs at the frontline, if they want (but i suspect they will be concentrated on HI). Ofc, i would leave a significant air support at your big hubs (Bangkok and nearby bases, Singapore, oil centers...)
Where is KB at the moment? perhaps you could set an trap for Greyjoy... showing him near Hokkaido (so he will be careful with his supply transprots and navy, and he will have to strenghten his CAP - what means less fts on sweep over HI)
After that you can run under the protection of one your bases.... if you get lucky he might attack KB. With KB fighters on CAP and support from land based FTs you might hurt him (i guess, not sure with this current air combat model).
Yes, I am moving many forces back to the home islands while simultaneously trying not to cripple my defense on other fronts.
I bet he could shut down several of the home island airfields as you say, but I think it highly unlikely that he could keep 4-5 interlocking size 9-10 airfields permanently supressed. And I would very much welcome the attempt, because it would take away from his strat bombing, which is much more deadly in the long run.
Yes, counter-invasion defense will consist of 3 elements:
1. The IJN ~ all major surface warships are now in home waters ready to pounce on an invasion.
2. Air attack ~ most of the Japanese air forces are in the home islands ready to respond.
3. Ground troops ~ all likely invasion beaches are being heavily reinforced
The problem is that there are so many possible invasion beaches that it's impossible to adequately guard them all, and that since he is comign from so close (even less distance than the cross-channel invasion at Normandy), it will be very tough to respond with air and naval forces in time to make a difference. We are concentrating ground troops on the "red" bases in the north, with air-sea response lile yot play more of a role in the southerly beaches.
A nasty thought just occured to me. If he landed at Sendai/Iwaki with a large enough force, he might be able to use his tanks to blitz straight into the base in the center of northern Honshu on the turn immediately following the invasion. I must be on guard about this possibility. I am reinforcing both that base (the high ground), and the adjacent beaches accordingly.
The allies have been absolutely dead quiet in all other theaters (appart from a minor overland skirmish in New Guinea near Lae). I suspect he has withdrawn almost all troops from everywhere on the map to maximize his force in Hokkaido for a Honshu landing (or possibly an amphibious operation vs. the Bonins/Ryukus/Formosa). I bet he has taken that 10,000 AV indian army around the world and it is now in Hokkaido. I know he has at least 2000 AV in the Solomons/NG, but other than that, he could have everything else in Hokkaido by now. Anyone have a guess to how much AV the Allies can amass in mid-1944 if it's all in the same place?
The KB is mostly split up out raiding supply lines (we've sunk about 20+ AKs in the last month or so, but not much to write home about actually - it is more of a diversion from the main show). I'm treating them a bit like the confederate cavalry under Nathan Bedford Forest trying to get around Sherman's army and attack the rear. While trying to avoid his carriers, I'm positioning them to interdict convoys leaving the US West Coast. In fact, I seriously considered (and am still considering) a port strike raid on a US West coast city. Might be a first for 1944.