The Empire of Japan, also called the Empire of Chireiden, is a nation in East Asia.
Japan was a peaceful nation. During the Tokugawa Shogunate it soon grew a bit unstable over time. In 1868 Tokugawa Yoshinobu managed to prevent Emperor Meiji from ending their rule, and thus the Tokugawa Shogunate continued. It then proceeded to last longer as time went on.
Soon by 1905 however Yamame Kurodani led a Subterranean conquest of Japan, starting in Hokkaido. Soon, she conquered North Japan (all of Hokkaido and 1/3 of Northern Honshu) and established the Empire of Japan. Afterwards, Southern Japan, still under the Tokugawa Shogunate, begun to grow unstable. Emperor Meiji demanded that Tokugawa end their rule, but Tokugawa Yoshinobu refused. Soon a civil war happened, and Emperor Meiji tried to flee to the North, but was killed by Yuugi Hoshiguma.
Tokugawa Yoshinobu then assumed role as Emperor and continued the Tokugawa Shogunate until his death in 1913 when he was succeeded by Tokugawa Yoshihisa. Though eventually Koishi Komeiji herself grew tired at how long it takes for Yamame Kurodani to conquer the rest of Southern Japan. In 1920, after much military build-up, Tokugawa Yoshihisa launched an invasion of North Japan.
Despite early successful battles, Yamame Kurodani, along with Yuugi Hoshiguma and Koishi Komeiji, managed to break their winning streak and soon Southern Japan was invaded. Realising that he can't win, Tokugawa Yoshihisa fled Japan and set up the Tokugawa Shogunate in Exile in Novo Airão, Brazil.
In 1922, the Tokugawa Shogunate officially had fallen as Southern Japan was conquered by Yamame Kurodani; though the Tokugawa Shogunate continues on in exile with-in Brazil.
Then in 1930, the new Empire of Japan conquered Korea, Papua New Guinea, Philippines, Australia, New Zealand, Chile, and Argentina in the 10 year war. Japan had won and annexed all those areas, as well as all the islands in the Pacific.
Japan also had established the League of Nations. With that, Finland, Russia, Mexico, Brazil, African Union, and Thailand had joined it. With that, Japan basically ruled the world, except for the faux European Union, China, Saudi Arabia, India, Egypt and Kentucky.
Over time, Finland-Japan relations declined as Reimu got greedy and begun to save up money for herself and didn't really use it to improve Finland. By 1968 Finland was kicked out of the League of Nations and Japan had cut ties with Finland. With no support, Finland soon found themselves annexed by the European Union in 1984.
Later, after Russia lost Iran after the Indians and Chinese and in 2007, due to Russia's humiliation of that war, it was annexed by Japan after Koishi used her Dark Heart power to absorb Russia.
While Mexico, Brazil, African Union, and Thailand maintain their independence and their ways, they all recognise Koishi Komeiji as their True Leader/Ruler.