Here the Skaven learned how to be ninjas. Except that they learned to be ninjas in Cathay. They were apparently united as a nation for the first time in 1IC by some guy named Yamayakyuki I who promptly dropped dead a few years later in 12 IC and since then the position of Emperor (known as the Divine Sun) has become mostly ceremonial similar to how the emperor position was in real life Japan during the Tokugawa Shogunate. They also have monks known as Vimto monks and they along with most of the population worship what’s essentially a Buddha-like deity known as the Orange Simca which was named after one of the Warhammer developers' car. The truly hilarious thing is that Simca is a French brand.
This is literally everything we know about Nippon.
In the early editions of the game there were three or four named Samurai and ninja type characters but nobody talks about them because they were generic and all stupidly named after Japanese cars. In the latest edition there are two known characters from Nippon: The Red Ronin and Lady Katsui, who lives in Marienburg. According to End Times, they've got the best fleet ever, but they don't do shit with it. It's the best fucking fleet in the world. That's right, not druchii black arks or asur dragonships, fucking Yamato-Class Battleships. The little official info on their land army pretty much shows it as being the same as what real-life Japan had during the latter half of the Shogunate (arquebus wielding ashigeru, peasant foot soldiers, samurai and ninja etc.) plus, rocket artillary, magic sorcerers, magic kung-fu monks and...suicide bombers called Kamikaze. On a less stereotypical note Ogres also apparently exist there somehow and are known as Oni, so you could probably convert some Ogre kingdom units in order to help support a homebrew Nippon army.
Genevieve Sandrine du Pointe du Lac Dieudonné went there once. Probably. If she exists. Honestly, this wouldn't be worth mentioning except that we don't know shit about Nippon so it's like 5% of what we know.
It is possible that they might show up in Total War Warhammer III, but we would advise against holding your breath on that...though GW hinted indirectly that while expanding Warhammer The Old World that they would visit other regions to revisit. Which means that Nippon is possible in the future.
Also, "Nippon" is literally the Japanese word for "Japan", because of course.
|Regions and Areas of the Warhammer World|
|Areas of The Old World:||The Empire of Man - Bretonnia - Albion - Estalia - Tilea - Kislev - Norsca - Border Princes - Worlds Edge Mountains - Karak Eight-Peaks|
|Areas of The New World:||Naggaroth - Lustria|
|Areas of The Eastern Lands:||Cathay - Nippon - Ogre Kingdoms - Dark Lands - Kingdoms of Ind - Khuresh - Eastern Steppes|
|Areas of The Southlands:||Nehekhara - Araby - Badlands - Marshes of Madness|
|Other Areas of the world:||Ulthuan - Athel Loren - Chaos Wastes - Skavenblight - Lost Isles of Elithis|
|Main bodies of Water:||The Great Ocean - The Far Sea - The Sea of Dread - Inner Sea of Ulthuan|