Taiwan is one of the most important entities for Japan in the international relations and history. Beijing government has emphasized “One-China Policy” and doesn’t recognize Taiwan as a sovereign state until the present. The issue, whether Taiwan is a de jure state, is a legal issue for only Japan based on the international legal systems of recognition and treaty. In those systems, it is evident for Japan that two peace treaties exist until the present with the Republic of China and the People’s Republic of China. The existence of two treaties means that two sovereign states who did battle against Japan in World War II exist.
Consequently, based on the legal system of recognition of government, Japan did not recognize “the change of recognition of government” in the Republic of China, but gave recognition of state to the People's Republic of China. As a result, the People’s Republic of China became independent from the Republic of China who succeeded the Qing Dynasty, therefore Taiwan is a sovereign state from standpoint of Japan according to the study of international law.
"A Concise Consideration on the Legal Status of Taiwan for Japan from the perspective of the Customary International Law of Recognition,"
Japanese Society and Culture: Vol. 1
, Article 4.
Available at: https://gensoken.toyo.ac.jp/japanese-society-and-culture/vol1/iss1/4