How do you get a 300 IC Japan? In my current game I have annexed China, taken the whole pacific and all of Indian and I am at about 270.
Honestly, it was Secret Master who taught me how to get 300+ IC as Japan. (Giving credit where it's due.) I use his suggestions about half the time when I play Japan, unless I'm feeling generous towards the US. Here is a step by step:
Before starting your game, do a production run of about 10x IC. This will both give you more IC and rapidly reduce the practical. It should take about 15 months if I recall or until March of 1937.
Meanwhile start making trades with the US to sell supplies. Start stockpiling energy/metal/rares because you will need them. I run my energy and metal at 25-30+ above what I need and rares 40-50+. People will say you don't need to do that but I always end up needing them. Trade with whoever you want but Soviets and US are good candidates.
When the game starts, withdraw all of your Japanese units from Manchuko to Korea (or wherever - I always put a few on mainland Japan).
When you're IC is done you can do another run of 10x (it should take less than a year now) or I prefer to 2x 5x because I want to start army/navy production. If you keep at least 4-5 IC in your production, it will keep your practical quite low.
Trigger the Marco Polo event and let Shanxi take Manchuko. After Manchuko falls, conquer Shanxi (now including Manchucko) and get all that beautiful IC.
Conquer NC, CC but don't end the war with XIC (or whatever it is). When you do, puppet them.
Keep going south - conquering - until you hit Hong Kong. All the while you're doing this, research all your IC techs. If you're in the Axis, and Germany declares on France, you can declare on France and get set a wargoal to conquer their Asian holdings as well. This will give you much needed rares. I also set a wargoal for Great Britains and Netherlands holdings but I've never actually seen them fall.
I generally stop building IC after I've made about 20-25 units (sometimes less), but I always end up with 290 to 300+ IC. I then puppet Australia and New Zealand.
I don't know how well this works in TFH (as I'm running my first game right now) but it works great in FTM.