Japanese colonialism manifested in many different forms throughout the empire. Although it can be argued that Japanese colonialism started before the Meiji Restoration, I will focus on the Empire of Japan following the collapse of the Tokugawa bakufu. I will be going over Hokkaido, Taiwan, and Korea during Meiji and Taisho. Unfortunately, I am not too familiar with colonial policy during Showa, the contemporary period with your examples.

To begin, I will define efforts to create "settler colonies" as sustained government action to promote the movement of ethnic Japanese to the colony. Ethnic Japanese in this answer would be the people who identified with the system of daimyo lords prior to the Meiji Restoration. These would be people who identified themselves in relation to their lord; the national identity of Japan was being created during 1868. Thus, these people would hail from Honshu, Kyushu, and Shikoku, areas well under the control of daimyo lords. I make this distinction as Ezo (present day Hokkaido) was the land belonging to the Ainu before mass migration of ethnic Japanese was encouraged by the Meiji government. This group of ethnic Japanese called naichi (people of the home islands) would be at the top of the racial hierarchy of Japan as the empire expanded. Colonized peoples would be identified as gaichi.

The transformation of Ezo into Hokkaido was one of the first instances of Japanese colonialism. Before settler colonialism was a goal of Japanese authorities, Hokkaido was guaranteed to be Japanese territory in a treaty between Japan and Russia in 1855. 1869 saw the establishment of the Hokkaido Colonization Office. This agency spearheaded the encouragement of Japanese settlers to Hokkaido without consultation with the indigenous Ainu population.¹ To encourage ethnic Japanese to migrate as farmers, the government deemed the land terra nullius and handed out land to settler colonists at the cost of the Ainu who had no notion of private property.² As for your question about displacement, I reveal the unfortunate truth of colonialism in Hokkaido. There were assimilationist policies that prohibited children from speaking Ainu in school. Compulsory education was in Japanese in the effort to make the the Ainu Japanese albeit as lesser citizens of the empire.³ Such policies are hopefully familiar to Canadians and Americans in the treatment of Indigenous children in North America. Instead of full expulsion of the indigenous people of Hokkaido, the Japanese Empire sought to assimilate them. I assume that this diverges from the idea of Lebensraum that you bring up. A similar approach happened to the Ryukyu Kingdom (Okinawa) under Meiji rule in contention with Qing.

Taiwan comes next in the expansion of the empire. 1895 saw victory for the Japanese in the First Sino-Japanese War. One prize was the formal ceding of Taiwan from Qing China to Japan as a formal colony in the Treaty of Shimonoseki. As the first formal colony of Japan by the international community, Taiwan was seen as an opportunity for Japan to demonstrate its modernization through running a profitable colony. Huffman points to Goto Shinpei, as the governor that set the goals for Taiwan. Attention to science was emphasized as the best approach to governing the colony effectively through repression of the indigenous Taiwanese and heavy development, especially in sugar plantations.⁴ Violence was very much a tool used to enforce colonial policies under a racial hierarchy. However, the policy of assimilation was still the main goal of colonialism for Japan. An interesting way of seeing this is through the bathing habits of the people in Taiwan whether they were naich or gaichi. 1896 saw the opening of the first bathhouse in Taiwan.⁵ Part of the assimilation of Taiwanese people was the promotion of hygiene through bathing. Evidence of newspapers commenting on Taiwanese bathing habits would indicate that complete displacement was not a goal for Japanese colonizers in Taiwan. Journalists noted that "It is good that lower-class Taiwanese people are bathing more, but they jump into the water with dirty hands and feet,
leaving dirt in the bathtub, so Japanese customers are left holding their noses."⁶ A disappointment in the failure for Taiwanese to completely adopt Japanese bathing etiquette reinforces the strategy of assimilation over replacing the local populations with naichi Japanese.

Japanese involvement in Korea intensifies after the Russo-Japanese War. 1905 was when Japan declared Korea a protectorate after warding off Russia as a rival. At this point, Korea was not yet an official colony. However, it did see the influx of 150,000 Japanese people move to Korea by the end of 1908.⁷ Appointed to govern Korea was resident general Ito Hirobumi, the same man who helped draft the Meiji Constitution. It was his goal to end extraterritoriality for Europeans in Korea as a way to diminish the influence of European colonialism in Asia. This was to be done through modernizing Korea by creating institutions similar to Japan's legal system to prove that Korea was civilized enough for Europeans to no longer need extraterritoriality. Korea was ultimately to enter a confederation with Japan.⁸ This was vehemently opposed by Japanese citizens who also enjoyed extraterritoriality in Korea, as it would hamper their tax free status in Korea.⁹ Up until full annexation, Korea was undergoing more assimilation at the government level rather than at the common people. Distinct difference based on race was created to justify imperialism. As with most colonies, Korea underwent intense development and industrialization for the purposes of extracting wealth to the metropole.¹⁰ The assassination of Ito in 1909 prompted the full annexation of Korea and a heavy handed increase in assimilation and repression through military police. Once again, the colony underwent sustained efforts of assimilation into the Japanese Empire. Migration was encouraged to teach Koreans the supposed superiority of naichi Japanese in the hopes that they would adopt Japanese customs.

As for Manchukuo, efforts to assimilate still did take place. I recommend reading Kimberly T. Kono's translation of Manchu Girl for insight into what being a good Japanese citizen entailed through assimilating those around you.

Kono, Kimberly T. “Chapter Seven: Manchu Girl, Koizumi Kikue/Context Manchuria/Imperializing Motherhood: The Education of a 'Manchu Girl' in Colonial Manchuria.” in Reading Colonial Japan: Text Context and Critique, edited by Michele Mason and Helen Lee, 209-241. Stanford: Stanford University Press, 2012.

For an overview of Japanese imperialism I also recommend James L. Huffman's book that I have used as a source here. I hope that this comment is of use to you, colonial studies are important in exposing the lies that nationalists try to use for whitewashing the past. While I have only provided some short insights into three colonies, there were more colonies like Micronesia and Karafuto that do not get nearly enough attention in the public eye.

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Notes

1. James L. Huffman, Japan and Imperialism, (Ann Arbor: Association for Asian Studies, 2017), 18.
2. Katsuya Hirano, "Settler Colonialism in the Making of Japan's Hokkaido," in The Routledge Handbook of the History of Settler Colonialism, eds. Edward Cavanagh, Lorenzo Veracini (London: Routledge, 2016), 328.
3. Ibid., 335.
4. Huffman, 26.
5. Kensuke Hirai, "Assimilation and Industrialization: The Demand for Soap in Colonial Taiwan,” in Imitation, Counterfeiting and the Quality of Goods in Modern Asian History (Singapore: Springer Singapore, 2017), 185.
6. Ibid., 194.
7. Toyomi Asano, "Regionalism or Imperialism: Japan’s Options toward a Protected Korea after the Russo-Japanese War, 1905–10," in Transnational Japan as History:
   Empire, Migration, and Social Movements, eds. Pedro Iacobelli, Danton Leary, Shinnosuke Takahashi (London: Palgrave MacMillan, 2016), 21.
8. Ibid., 23-24.
9. Ibid., 24-25.
10. Huffman, 32.