What was the citizenship of Taiwanese people during the Japanese colonial period?

This is a very good question. Before trying to answer this question, some details should be pointed out.

(1) Taiwan was ceded to Japan by Qing Dynasty China in 1895. Following the 1895 Treaty of Shimonoseki, Japan exercised sovereignty over Taiwan and held title to its territory.

(2) The period beginning in 1895 was not a Japanese occupation of Taiwan. Taiwan was ceded to Japan. "Military occupation" and "territorial cession" are different.

(3) The dates you have given here, for the period of 1895 to 1952, are correct. Taiwan was not returned to China in 1945. None of the Allies recognized any transfer of the territorial sovereignty of Taiwan to China upon the surrender of Japanese troops in Taiwan on Oct. 25, 1945.

(4) The date of Oct. 25, 1945, only marks the beginning of the military occupation of Taiwan. General Douglas MacArthur directed Chiang Kai-shek (of the Republic of China) to go to Taiwan and accept the surrender of Japanese troops. Those directions were contained in General Order No. 1 of Sept. 2, 1945.

(5) The surrender ceremonies were conducted on behalf of the Allies, however the ensuing military occupation of Taiwan was conducted on behalf of the principal occupying power -- the United States of America. Hence, at the most basic level, the ROC in Taiwan is a "subordinate occupying power."

(6) The 1946 announcement of the mass-naturalization of native Taiwanese persons as "ROC citizens" in occupied Taiwan territory is a war crime. (Hence, in the present era, to classify native Taiwanese persons in Taiwan as ROC citizens is incorrect under international law.)

(7) In the post-war treaties, the territorial sovereignty of Taiwan was not awarded to the ROC, or to any governmental entity on Taiwan. Hence, the ROC on Taiwan is not a sovereign nation, and cannot enter the United Nations. (Likewise, since "Taiwan" is merely a geographical term, and not the name of a country, "Taiwan" cannot enter the United Nations either.) According to the post-war San Francisco Peace Treaty of 1952, Taiwan remains as occupied territory of the United States of America.

NOW, turning to your question about the nationality of Taiwanese people during the Japanese colonial period --

As a preliminary remark, you have to consider that the United States is a very advanced nation, but before the early 1950's in the United States is was not common for people to carry passports when travelling to other countries. (In fact, the original version of the US Immigration and Naturalization Act was only promulgated in December 1952.)

Hence, it may very well have been the case that through most of this Japanese colonial period the Taiwanese people did not carry any sort of formal passport when travelling overseas. They may have carried some other type of paperwork or simple identification documents. (I am sorry that I do not have the definitive answers to these questions. I have previously searched on some Japanese websites for this information but without success.)

What we can say for certain is that the Taiwanese people did have Japanese nationality during this period, up until the Spring of 1952.

According to my associate's inquiries with the Japanese government, the Japanese nationality of Taiwanese persons was cancelled by the Japanese government in early 1952, with the knowledge that the San Francisco Peace Treaty was soon to come into effect. In that treaty, Japan renounced all right, title, and claim to "Formosa and the Pescadores," but no receiving country was specified.

THE PRESENT ERA

Under international law, it appears (on the surface) that the Taiwanese people are stateless. As explained above, in the present era it is incorrect to classify the Taiwanese people as ROC citizens.

There is however a very coherent, but little known explanation under international law to say that native Taiwanese persons in the present era should be classified as "US national non-citizens."

ehh, you got the time wrong, Taiwan was returned to the Chinese government at the time right after the Japanese surrendered un-conditionally in 1945. You could check with some historic societies in Taipei to see if you can get any answer for your question. The only thing I know for sure is that not that many people had passports at that time.

Prior to 1895 they were part of China and they were reverted back to China after world war II. Now they want to be independent for China.

Being under control of another country doesn't change the citizenship of the country. It only changes when it become a independent nation and they set policy.

I don't know, but I find it hard to believe they had equal rights or something of this kind under Japp occupation.