Culture in Japanese style. With new mechanics

[small charm]

The question is, what feature would they get?
Perhaps this culture could be more sea-oriented, having a unique area that gives many bonuses. Also at sea, their units become stronger.

Or, along with culture, add spy mechanics to the DLS. Thanks to this, you can see an overview of the enemy city, destroy buildings, and cause damage to units inside. The Japanese have ninjas for this purpose.

As an example of spy mechanics, you can take Endless Legends. But modify it with your own characteristics

[eager vault]

I'd rather have this as a thematic something.

As in, just make the armors and the city, allow it to paste it onto other cultures. It could add a lot to faction uniqueness.

[high goblet]

or if triumph decides to add subcultures to other cultures besides primal

we could have eastern subculture for feudal that exchanges the knight for a samurai mounted archer

and defenders get replaced by elite yari ashigaru

[eager vault]

Just an example. The only thing missing were the structures, really.

As in, cities.

After the aesthetic was set, tomes and traits did most of the heavy lifting. You had tier 1-2 infantry throwing pila at the enemy, and pretty decent gameplay relying on formations.