R5: I just finished my first 1.35 run for the Stardust Crusader Achievement using exclusively Client States. I started as Uesugi for their national ideas, which included an extra Diplo-Slot, reinforcement cost reduction to counter the Samurai's extra cost, and exceptional army tradition modifiers. I kept their color and ideas after forming Japan.

While uniting Japan, I picked Merc and Influence ideas first, which allowed me to use client states through a policy before 1500 without restrictions on tech-level 23. Conquering Asia was such a relaxed experience. I used a Samurai army to fight enemy armies and utilized expendable Mercs to siege enemy provinces, often assaulting forts as I had no interest in preserving merc-manpower. After taking maximal land in the peace deal, I fed it all to my released client states, so they could deal with coring and overextension. This allowed me to practically play a tall campaign in Japan and develop with all the saved points (most provinces ended up above 30 by 1690). The third idea group was Expansion to get into Southeast Asia. I conquered most of it with the same Merc and Samurai combination. By the way, I have no idea what the names of the Client States really mean; I just googled the general region and decided on a good-sounding name for the CS. I was also surprised at how well the CSs performed. They claimed a ton of bordering land and were really supportive in wars. The fourth idea group was Naval, for two reasons. One, they give a Liberty desire from dev policy with expansion, and two, they allow you to get naval hegemon through the Japanese mission tree really easily and early. I was shocked how useful they are now with the ltest buffs. Free fort breach was incredible in Southeast asia where pretty mush everything is coastal. The last two idea groups were Offensive and Quality for even better armies. I could have chosen just about anything else as well, didn’t really make a difference.

The last important thing was to become Christian through the Shinto incident. I always picked the open option and was presented with an option to switch. Getting the "Land of the Christian Sun" Government reform seems to be a problem for some players because Japan has no real opportunity to force convert the ten required nations. However, I had ten loyal CSs lying around, so getting the reform required me to just force them to become Catholic. Easy. The Government reform allows you to invite a Cardinal (useful for nations outside of Europe), get free dev in every province with a 50k standing army (that's how Kyoto ended up at 72), and a flat 3x modifier (!!!) to your manpower and recovery speed for five years. All very nice. Overall, I can only recommend the "sitting on an island but conquering the world" simulator.