Puppet States & Conquered Territories

As a fledgling empire, Japan has dominion over lands of other cultures and races. The government takes a carrot and stick approach with governance, where they try to make integration and cooperation as palatable and rewarding as possible, while also brutally suppressing dissent. It is through this process that the government tries to push its citizenship program to incorporate loyalists and moderates into the fold to encourage them to assist in the suppression of subversive elements.
Only natural born Japanese have citizenship and voting rights within the empire, and imperial subjects outside of Japan often find themselves treated more as resources rather than valued members of the empire.

Korea & Formosa

Korea & Formosa was annexed by Japan during the 1st Sino-Japanese War in 1894, which Japan won. Both were previously under the Chinese sphere of influence, but have since been incorporated into the Japanese Empire. Despite having been under the empire's rule for several decades, the mistreatment of the subjects in these regions has led to a rise in subversion and terrorism, especially in Korea.

South Sakhalin & Kuril Islands

Acquired during the Russo-Japanese War won by Japan, these sparsely populated frigid land acquisitions previously held by Russia were meager compensation for the hard won victory for many Japanese.

Marshall, Caroline, Marianas, Palau, and Waiapi Islands

As a reward for fighting on behalf of the allied powers in the Great War, Japan seized these south pacific island chains from their previous German imperialist owners. These islands greatly increased the naval and aerial power projection Japan could field in East Asia, cementing it as a major power in the region.

Manchukuo

While not technically owned by Japan, Manchukuo was annexed by Japan after the Mukden incident, a false flag attack on a Japanese railroad that served as the impetus for Japan to invade and seize the Manchurian region of China. After successfully seizing the territory from China the Japanese established a puppet government to try to make the annexation seem like it was more legitimate and not a power grab, a maneuver that did not fool the rest of the world. The leadership of this new "independent" Manchurian state was comprised of the deposed Qing dynasty that ruled China until a revolution in the 1910s that sought to liberalize and modernize China. The Qing dynasty was seeking to reinstate their power, and the dynasty was originally from the Manchuria region, so they became the obvious choice to rule this new nation, but only under Japanese guidance and involvement. The last emperor of China, Puyi, is now the emperor of Manchukuo, and a subservient vassal of the Japanese government.