I like made speculation for fun, so, maybe this one gonna be the first of many post of this topic. I sincerely believe that the Japanese are the most likely civilization of Eastern Asia to enter after China and Mongolia, I have other preferences to see before, but it seems important to me anyway. In principle, you have to see what feudal Japan was like, to see how to translate it:
-The feudal Japanese had their nation divided into a series of fiefdoms dominated by clans whose leader was a warlord named Daimio. Its economy was based on the cultivation of rice, fishing and purely maritime trade with neighboring nations.
-In war they stood out for the belligerence of the samurai, a warrior social class trained in martial arts based on the use of weapons. The ranks were swelled by the Ashigaru, peasants who were supplied with weapons and equipment to go to war, initially they were not paid and they took everything from looting. Shields were not widely used in medieval Japan, nor were crossbows (for native production issues) beyond ballistae that served as artillery.
-Every new town center spawns a Cherry Orchard (count as berry bushes).
-Villagers gathers 15% faster from berry bushes and 15% slower from animals.
-Fishing Ships gather 5% per age (starts in first age) to a maximum of 20%.
-Military buildings cost -30%.
-Shrine: Structure that attracts animals and generates gold according to the amount it has attracted, each sanctuary supports a limit of animals. Avialable in first age.
-Dojo: Military structure that train units from the barracks, archery range or stable free but at verry slow time.
I could mention more units, but many of them are simply a reskin of others or carry a specific name to denote that certain bonuses and technologies affect them.
To age II
Heian Palace: Acts as a town center but 50% faster in everything and shoots an aditional arrow.
Tori Gates: Heal nearby units.
To Age III
Rokuonji Temple: Acts as a x3 full animal shrine and can garrison one relic to produce 50% more relic gold.
Himeji Castle: Strong fortress, can train samurai units 50% faster.
To Age IV
The Shogunate: A verry strong fortress, elevates the Daimio limit in one and trains it 100% faster.
Capital (E.d.o) Palace:* Reduce the cost of every tech in 20% and gain acces to the next technologies: Naval reforms, Shogun
Every time the Japanese advance to the next age gains a clan alliance, every clan provide their own bonuses but it makes it impossible to ally with the other options of the same age.
-Archers +1 of damage.
-Archery range works 10% faster.
-Allow the recluitment of samurai archer (archer with more armor).
-Ships gains 15% more hit points.
-Fishing ships and trade ships moves 20% faster.
-Ashigaru units -20% cost.
-Ashigaru units +10% hit points.
-Stable units and Yabusame Samurai gains 10% hit points.
-Stable units and Yabusame Samurai moves faster.
-Stable units and Yabusame Samurai -10% cost.
-Monk automatically upgrade to warrior monk, a infantry monk with naginata (canty cavalry pole-arm).
-Unlocks recruitment of Naginata Samurai (Anty cavalry samurai).
-Katana samurai gains 15% more hit points.
-Katana samurai gains +2 attack.
-Katana samurai -10% cost.
-Artillery siege units deals 20% more damage.
-Artillery -25% cost.
-Artillery +1 range.
-Allows the recruitment of T.a.n.g.a.s.h.i.m.a samurai.
#################### units +1 range.
#################### units +3 of damage.
-Allows the recuitment of No-Dachi Samurai.
-Infantry gains charge damage bonus.
Well, is time to start talking about the roster (some units are clan options exclusive):
-Yari Ashigaru: A sperman reskin. Age I
-Katana Samurai: Replaces the man-at-arms, have less armor but high attack speed. Age III
-[Uesugi Naginata Samurai]: Anty cavalry samurai. Age III.
-[Date No-Dachi Samurai]: Samurai with melee area of damage. Age IV.
-Ashigaru Archer: Archer reskin. Age II
-Samurai Archer: Archer with more hit points. Age III.
-Yabusame Samurai: Horse archer with a little bit higher armor. Age III.
-T.a.n.g.a.s.h.i.m.a Ashigaru: Handgunner reskin. Age IV
-T.a.n.g.a.s.h.i.m.a Samurai]: Handgunner with more hit points. Age IV.
-Ashigaru Horseman: Reskin of the Horseman. Age II.
-Samurai Cavalry: Cavalry with lower charge attack and armor than the knight, but faster attack with sword. Age III.
-Daimio: Similar to the Khan but in melee. Nearby units gain speed and damage.
-Monk. Age III
-Shinobi: With a lot of melee attack, a short range shooting attack every 12 seconds, with the ability to scale walls and enter in stealth mode.
-Kataparuto: Mangone reskin. Age III.
-Cannon: Bombard resnkin. Age IV.
-Bo-Hiya: Soldier with roket launcher. Age IV.
-Ōyumi: Springard reskin. Age III.
-Trade Ship. Age II.
-Kobaya: Archer ship with less hit points than other, but shoots two more arrows. “Simple archer ship, with very few protections but with a deck that allows shooting more easily.” Can be upgrated to T.a.n.g.a.s.h.i.m.a Kobaya with a unnique tech.
-Bune: Slower springard (or Ōyumi) ship, but with more hit points.
-Nihon-Maru: Slower artillery ship, but with more hit points.
-Bushido: Military buildings works 15% faster.
######### parachute:* Inflatable cape like a parachute, which protects from arrows from behind. Gives +1 armor against missiles to samurai cavalry.
-Atakebune: Bunes now shot arrows in short range betwen ballista shots.
-Naval Reforms: Kobaya of Archers upgrate to Kobaya of T.a.n.g.a.s.h.i.m.a
-Feudal Clans: Villagers works 15% faster in rice farms.
-Kami Celestial: Temples with relics and shrines produces 10% more gold.
-Hermit Of The Mountains: Monk and Warrior Monk with 20% more hit points.
-Shogun: The daimio becomes a Shogun, gains more armor and double range aura.