Who he was
Evidence grade: Traditional · Later accountsAlmost everything known about Denshichirō is a few lines of the 1654 monument. His name is written 伝七郎, Denshichirō. The monument calls him a Yoshioka and says nothing else about him: no age and no father.
The monument does not say he was Seijūrō's brother. A Kumamoto book of 1755 calls him a younger brother of the house, and one of 1776 calls him a powerful fighter. Both were written 150 years or more after the event. The film does not claim the two men were brothers.
No description of his face, build or clothes survives. The film's picture of him is a design.
The road to the fight
Evidence grade: Traditional · Later accountsAfter Seijūrō, the monument says, Denshichirō "again" came out to settle victory and defeat. The place is only "outside the city". It does not name the ground.
He came, the monument says, with a wooden blade of over five shaku. A shaku is about 30 centimetres, so the blade was more than about a metre and a half. The monument does not give the exact length.
The monument gives no reason beyond settling the contest. The 1716 book on the Yoshioka does not mention this bout at all. A later Kumamoto story says Musashi turned up late to both of the first two bouts and wore the Yoshioka down by waiting. That story is legend, and it is not in the monument.
The date is the same calculation as the first bout: about 1604.
The contest
Evidence grade: Traditional · Later accountsThe monument is short. Musashi, "meeting the moment", took that wooden blade from him and struck him. Denshichirō fell to the ground and died on the spot.
That is all the source says. No source says how the blade was taken, where Musashi stood, or what he held in his hands. A book of 1776 says he was killed in one blow and calls him a powerful fighter, but that is colour added 120 years after the monument.
The film shows how the blade is seized. That movement was invented for the episode. It was designed from a teaching in the Fire scroll of Musashi's own book, "hold down the pillow", which is about watching for the start of an opponent's strike. The source says only that the blade was taken, and that it ended in a death.
After, and how we know
Evidence grade: Traditional · Later accountsThe monument is the only early account of this bout. The Kyoto-side telling in the 1716 book is silent on it.
Silence does not prove the bout did not happen. But we have one source, from Musashi's family, written about 50 years afterwards.
The monument goes on to say that the Yoshioka martial house was finished. Other records say otherwise, and Denshichirō is not named in them.
The monument states his death plainly. We treat that with the same caution as everything on this stone: it is the account of his opponent's family.