The Book of Five Rings
According to the introduction of "The Book of Five Rings", Musashi states that his first successful duel was at the age of 13, against a samurai named Arima Kihei who fought using the Kashima Shintō-ryū style, founded by Tsukahara Bokuden (b. 1489, d. 1571). The main source of the duel is the "Hyoho senshi denki" ("Anecdotes about the Deceased Master"). Summarized, its account goes as follows: