The purpose of this paper is to use historical materiology to study the reliability of the personal history of Toru Shirai as described in Tenshinden Shirairyu Heiho Tsukaikata, written by Shirai’s disciple Okunojyo Yoshida. To do so, we clarify the descriptive form and contents of the biography, the source of the information used by Yoshida to write the history, and we verify the truth of the content.
The conclusions of this study can be summarized as follows:
1) The biography of Toru Shirai as described in Tenshinden Shirairyu Heiho Tsukaikata is based on what Shirai himself wrote in Heiho Mitchishirube. However, information about Shirai’s birth and social position were added to the beginning, information about his experiences that occurred after Shirai wrote Heiho Mitchishirube were added to the end, and anecdotes about his kenjutsu practice after age 8, including his matches against swordsmen from different schools, were inserted in the middle of Tenshinden Shirairyu Heiho Tsukaikata.
2) The added information is described in concrete terms, and some of it must have been communicated directly from Shirai to Yoshida. Judging from the related sources, Yoshida seems to have kept records of what Shirai said. Therefore, details of Shirai’s birth, social position, and anecdotes about his kenjutsu practice and so on must have been described based on Yoshida’s records. In that sense, the added information can be said to have a fairly high reliability as a historical source.
3) As a result of the detailed verification of the truth of Shirai’s birth, social position, anecdotes about his encounter with the ascetic Tokuhon, and other matters, it has been proved that most of the information is true. We can, therefore, conclude that Shirai’s personal history in Tenshinden Shirairyu Heiho Tsukaikata, written based on Heiho Mitchishirube that Shirai himself wrote and what Shirai said, has a fairly high reliability as a historical source from the standpoint of historical materiology.