Miyamoto Musashi later wrote that he fought more than sixty times and never lost. The first, he said, was against a grown man called Arima Kihei, when he was thirteen. The episode tells that fight as a later account describes it, then shows how much of it the older sources support.
The fight follows a book written in 1727, about 130 years after the event. The episode then sets it beside Musashi's own words and the 1654 monument. Faces, movements and anything else no source describes were invented for the film.