Adding Mission Trees to each countries will make the mod much more interesting, but that's tons of work.

Some random suggestions:

• Touhou Military Tech Group/Units, even if just renames of normal asian units choosing between Blue Fairy/Red Fairy is more thematic than Asian Offensive Footsoldier/ Asian Defensive Footsoldier.
  
  
• Touhou culture only estates, either in addition to or as replacement of the normal ones. Something along the lines of Humans, Yokai, Divine?
  
  
• Redone/more government reforms.
  
  
• As David mentioned missions would be neat.
  
  
• Events or mission rewards spawning famous characters for your nation as cheaper advisors/generals etc.

If you need help with anything send me a message, I enjoy messing around with the code but lack the ambition to publish anything of my own :p

These are some neat ideas to begin with :D

Regarding of government reforms I made some new ones for some of the Touhou nations. They are pretty experimental (and probably broken as hell, but this is somewhat the entire theme of Gensokyo) and fun to mess around with.

I also reworked some ideas, because some of these felt to generic, and added also some description to them. There are also some missions I'm working at, but this will take its time...

To your offer to help: I could really use some help with creating the unique unit type and especially the estates with its own disaster if possible ^^
I am thankful for every support :D

I do want to see a dynamic province naming from other european nations like the Spanish, French, Germans, Ect if they somehow did get to the island and conolized it since you already have some english province names and a "Human" nation there.

Once you unite Gensoukyo add a decision that gives you a casus belli on anyone you can see and reveals the world.

I'm working on events names for the case if Japan or the Europeans set a foot on Gensokyo, so dynamic province naming is definetely a neat idea.
Also events and decions are planed for exploration of the entire world. About the CB against everyone... well I'm testing it out. It makes some national ideas completely obsolete however.

Could you make Gensoukyou as an independent continent (separate from east asia)? In that case, we can set up trade companies out of Gensoukyou.

I intended to enlarge Gensokyo anyway to make more room for new nations and possible impactful events. With that said I appreciate your suggestion and will make Gensokyo an own continent :D

I think the gensokyo can be made like HRE or 日本幕府, so that the hole gensokyo can defense the invasion from Japan (but it seems the hole Japan cannot defeat even 1/4 gensokyo). And until anyone annex the 大結界 could he declare war on foreign countries.

Maybe some missions about Japan can be added for Fujiwara no Mokou based on the history of Fujiwara.

Yeah, I've observed the same results with Japan AI trying to get on Gensokyo, takes one province and the entire land is in a coalition against Japan / the Shogun. I'm not sure how I could make Gensokyo like an own HRE, but I will see what I can do. I could make a Shogun style of a gensokyan empire (I don't who shoud get the Shogun title tho)... nonetheless I will test some stuff out.

Regarding Fujiwara, fun fact: there are 2 secret events if you annex Fujiwara as a japanese nation.
I like the idea of special missions for Japan regarding Fujiwara though and will definetely add these.

I think most of Gensokyo (except for a few nations), should use Japanese unit models instead of general aisian, as from what I can tell Gensokyan culture is more like Japanese culture with some western European influences.

I really like this idea and I will make this happen.

I think it would be nice if gensokyo included the area requirement of institutions that needed special area requirement. especially, I want to see Colonialism is appear in gensokyo.

I hope there can be more factions added, but that need a bigger map, which seems a hard work. If you are interested in that ,we can talk in detail.Here is some other suggestion:
As I did in the old version mod, I still hope to revise the religion. There should be emphasized difference and conflicts between Hakurei Shinto and Moriya Shinto. As I understand, Reimu is lazy in spreading her faith, but Sanae is hardworking in comparison. So Moriya Shinto should be a more “aggressive” religion with higher missionary strength and more missionaries, and Hakurei Shinto should be more inclusive instead.
Some detailed suggestion about Moriya Shinto:
1.Have the mechanic as protestant with church power(with rewrote name) and optional buffs; or have deities as Hakurei Shinto, but only two deities with stronger but narrower buff than Hakurei Shinto
2.Higher basic bonus on Missionary strength or numbers& lower tolerance
3.Create decisions and holy lands to both Hakurei Shinto and Moriya Shinto to boost their Missionary strength (like Christian group)
4.If Moriya Shinto is added, I think it should be state religion of Moriya clan, Kappapolis, Tengu realm, Youkai Forest and Chireiden.
Some other suggestions about other religions:
Th Taoist has +2 Heretic Tolerance and +20% religious unity, but Th Buddhism has +3 Heretic Tolerance and +40% religious unity, that makes Th Taoist seems totally defeated. It should have its own advantage. I think Th Taoist should have a mechanic of harmony as Confucian, and has a +2 Tolerance of Heathen instead of +20% religious unity.

Adding new religion might be a too big change. There is some suggestions of small change:

1.The government of fairies should be more like a republic rather than monarchy, as there are many other fairies can challenge the rule of Cirno. There can be a election event to make Cirno, Daiyousei, Sunny, Lunar, Star or even Clownpiece Ruler. But royal marriage should be allowed.

2.Fairies are immortal, but Cirno and Daiyosei don`t have it. If you keep fairy government a monarchy, then that is necessary. And the skill of Cirno from the event is kind of too high, there`s nearly always a Cirno with more than 12 total skill points, which is weird. I think having a low skilled Cirno at the beginning and improving her skill by events or completing missions should be funnier ww.

3.The heir of Hakurei Shrine. Making Hakurei clan and Moriya clan theocracy is good, but I simply feel weird with a male heir of Hakurei clan. Sanae is immortal but Reimu is not, so the inheritance of Hakurei Shrine needs to think of. I think it could be like monastic order, gives three optional 20 years old females as heir by event. The last name Hakurei should be inherited. Actually Shrine maiden is not allowed to marry, but just allowing it is better. XD

4.About Marisa and Forest of Magic. Marisa is not immortal but she`d love to, so there could be an event to choose whether she becomes immortal or not. For the mission tree of FOM, I think it can include the following:
I. “Get fully access to Voile Library” Requirement: Own Scarlett Mansion Reward: Idea cost/Tech cost (and/or claims if you want, same for below)
II.”Control Kappa Technology” Requirement: Own all Kappapolis area; annex or vassalize Kappapolis Reward: Institution spread speed/Tech cost/Fire damage
III. ”Claim Makai” Requirement: have Alice as ruler or heir; Allied or Rivaled Makai Reward: A CB to create PU with Makai. (and also add a new decision to inherit Makai)
That`s all for now. I can give you more if you wish.