I have written biographies of modern Japanese politicians, including Ito Hirobumi, Hara Takashi, and the Emperor Showa. Through my studies, I have revealed how modern Japan have accepted international law and order, and how it has approached subjects concerning national security, the ruling of colonies, and the development of a constitutional monarchy.

For example, many researchers claim that the Emperor Showa was responsible for starting the Pacific War, as he had the constitutional power to stop it. However, using newly released materials, I have shown that the Emperor did not have sufficient power to prevent the war, and he was perpetually agonized over the extent to which he should intervene in political affairs in order to maintain peace. I have therefore concluded that the Emperor Showa had no responsibility for the War. This research has been commonly accepted in the field of Japanese history.