My Japan air power focus branch would look something like this (I slapped this together in Paint in 10 minutes OK...)
As for what "Army Aviation" and "Navy Aviation" would give you, I'm not sure. Perhaps both give you 1x -50% air doctrine boost and unlocks certain air power theorists that correspond to that service (IJAAS or IJNAS). Currently you can choose whoever to throw in there.
"Army Air Support" would give you 1x -50% boost for TAC and 1x -50% boost for CAS.
"Expand the Rikko Units" would give you 1x (maybe 2x?) -50% boost for NAV. Or maybe 1x -75% boost for NAV.
I don't know, I'm just throwing some stuff out there. Fine tuning (what a specific focus would give you) aside, this would certainly make far more sense than what we currently have.
I had a sleep. Here are a few revisions:
-I would add the word "Prioritise" to the front of both "Army Aviation" and "Navy Aviation" to better reflect history (and what I'm getting at). The historical path would be prioritising naval aviation. The IJAAS was always the junior service, and was slavishly subordinated to the IJA ground forces (doctrinally and even in terms of command structure). The IJAAS historically never had any serious independence push or loud and successful voices for more autonomy.
-I would change the name of "Unified Fighter Development" to "Unified Aircraft Development."
This air focus branch would better reward people for going down it. Right now the branch doesn't feel that good because it doesn't make much sense historically and it is mostly about removing a bad trait rather than giving you anything (other than two meh aircraft designers that should probably just be available at the start). As such Japan falls far behind what it did historically due to the way in-game research works, where you need to research every tech twice to get both the land-based and naval variants. With the tree above Japan would get the bump up to about 1940 tech (overcoming the flat penalty with boosts) before the player would need to grind for 1944 without boosts. This would encourage the player into a set of reasonably historical choices:
1. Spend extra PP and time removing the +10% research time penalty before researching higher techs, of course taking away from going down other parts of the focus tree earlier.
2. Just try to grind through the penalty and slowly research 1944 without boosts.
3. Stick with 1940 tech for the most part, relying on new variants to try and keep somewhat competitive.
All those would lead to a late-game USA advantage in aircraft tech without crippling Japan out of the gate (getting to 1940 tech).
I don't know if this is something @podcat would ever consider, but yeah. I kept the number of foci to the same number currently in the tree.
