Sasaki Kojirō

Sasaki (right) engages Miyamoto Musashi on the shores of Ganryū Island.

Sasaki was a long-time rival of Miyamoto Musashi, and is considered (by Musashi himself) the most challenging opponent Musashi ever faced. There are a number of accounts of the duel, varying in most details except the essentials, such as Kojirō's defeat. The age of Kojirō is especially uncertain – the Nitenki says that during his childhood, he

...  received the instruction of Toda Seigen, a master of the school of the short sword, and has been the partner of his master, he excelled him in the wielding of the long sword. After having defeated his master's younger brother he left him to travel in various provinces. There he founded his own school, which was called Ganryu.

The Nitenki's account initially seems trustworthy, until it goes on to give the age of Sasaki at the time of the duel as 18 years old; it is known that two years earlier he had been a head weapons master for a fief – but then that would imply he had reached such a position at the age of 16, which is extremely improbable. A further complication is that Toda Seigen died in the 1590s. This unreliability of the sources means Sasaki's age could have varied anywhere from his 20s to as late as his 50s. Even worse, a number of scholars contend that identifying Seigen as Kojirō's teacher is a mistake and that he was actually trained by a student of Seigen's, Kanemaki Jisai. The reason for this was that the person interviewed for the Nitenki (the last known witness to the duel) said Kojirō's age but the author missed the first part, and only got the last part which was 18 (十八), pronounced as "juu hachi" - however, numbers in Japanese are spoken as tens and ones, such as 48 (四十八) "yonjuuhachi". The reason his last name is Sasaki can be because of two reasons:

• His mother was a member of the Sasaki clan and had him out of wedlock. Since they were not married, he took on his mother's last name. She later married a distant cousin who also shared the same last name, and raised him as his own son.
• His mother was unaware she was pregnant with him when she married into the Sasaki clan. Thus, her husband, although suspecting the child wasn't his, raised him as his own son.

Like his adversary Musashi, he was also very tall (about 5  ft. 10 in. or 1.78 m), a giant compared to the average Japanese at that time.

Apparently, the young Musashi, at the time, around 29 years old, heard of Sasaki's fame and asked Lord Hosokawa Tadaoki, through an intermediary, Nagaoka Sado Okinaga, a principal vassal of Tadaoki, to arrange a duel. Tadaoki assented and set the time and place as 13 April 1612 on the comparatively remote island of Ganryujima of Funashima, the strait between Honshū and Kyūshū. The match was probably set in such a remote place because by this time Sasaki had acquired many students and disciples, and were Sasaki to lose, they would probably have attempted to kill Musashi.

According to the legend, Musashi arrived more than three hours late and goaded Sasaki by taunting him. When Sasaki attacked, his blow came so close as to sever Musashi's chonmage. He came close to victory several times until, supposedly, he was blinded by the sunset behind Musashi, who struck him on the skull with his oversized bokken, or wooden sword, which was 110 centimetres (43 in) long. Musashi had supposedly fashioned the long bokken, a type called a suburitō due to its above-average length, by shaving down the spare oar of the boat in which he arrived at the duel with his wakizashi. Musashi came late on purpose in order to psychologically unnerve his opponent, a tactic he had used on previous occasions, such as during his series of duels with the Yoshioka swordsmen.

Another version of the legend recounts that when Musashi finally arrived, Sasaki shouted insults at him, but Musashi just smiled. Angered even further, Sasaki leapt into combat, blind with rage. Sasaki attempted his famous "swallow's blade" or "swallow cut", but Musashi's oversized bokken hit Sasaki first, causing him to fall down; before Sasaki could finish his swallow cut, Musashi smashed Sasaki's left rib, puncturing his lungs and killing him. Musashi then hastily retreated to his boat and sailed away. This was Musashi's last fatal duel.

Among other things, this conventional account, drawn from the Nitenki, Kensetsu, and Yoshida Seiken's account, has some problems. Kenji Tokitsu discusses a number of obscurities and counterintuitive claims that have been identified in the account by him and previous scholars. Would Musashi only prepare his bokuto while going to the duel site? Could he even have prepared it in time, working the hard wood with his wakizashi? Would that work not have tired him as well? Further, why was the island then renamed after Sasaki, and not Musashi? Other texts completely omit the "late arrival" portion of the story or change the sequence of actions altogether. Harada Mukashi and a few other scholars believe that Sasaki was actually assassinated by Musashi and his students – the Sasaki clan apparently was a political obstacle to Lord Hosokawa, and defeating Sasaki would have been a political setback to his religious and political foes.

The debate still rages today as to whether or not Musashi cheated in order to win that fateful duel or merely used the environment to his advantage. Another theory is that Musashi timed the hour of his arrival to match the turning of the tide. He expected to be pursued by Sasaki's supporters in the event of a victory. The tide carried him to the island, then it turned by the time the fight ended. Musashi immediately jumped back in his boat and his flight was thus helped by the tide.