Sasaki Kojiro (佐々木小次郎 Sasaki Kojirō) is an antagonist in Ryu ga Gotoku Kenzan!
A man shows up to defeat Musashi when he is trying to flee from the treachery at the temple after the Sekigahara incident in which he was tricked into killing Tokugawa Ieyasu's son Yuki Hideyasu. This man gives the name Sasaki Kojiro. With his long dachi and Shinkage-ryu attacks, Musashi finds in Kojiro an opponent he cannot defeat. He decides to live to see another day and flees, but will always wait for a chance to fight this fierce rival again.
Ryu ga Gotoku Kenzan! Edit
Later, Kojiro appears in the Gion district in which Musashi is hiding under the assumed name, Kiryu Kazumanosuke. More treachery seems at hand, and Kojiro's appearances are brief but seem to revolve around the young girl, Haruka, who hired Kiryu to get revenge on the man who killed her family.
When Kiryu faces off against Kojirou at last at Kiyomizu Temple as Kojirou holds a sword against Haruka's neck, Tokugawa Ieyasu intervenes. Kojirou cannot go against his old lord, and withdraws. Ieyasu points Kiryuu to the village of the Yagyu family, telling him to ask for Yagyu Sekishusai, who will explain everything to him.
Indeed, he does. It turns out that Yagyu Muneyoshi, also known as Sekishusai, patriarch of the Yagyu clan, is Kojiro's father. Munenori is his real name.
Munenori has forsaken the way of the swordsman, leaving his village with the Shinkage-ryu skill taught to him by his father. In order to build a han for the clan (a domain recognized by the Tokugawa bakufu--quite a powerful asset), he has decided that he would need to become part of the forces conspiring to change the world. Namely, he decided to join up with Nankobo Tenkai, chief advisor to Tokugawa Ieyasu. But, as his father has noticed, Munenori has become a mere puppet in the hands of Tenkai and now struggles, carrying out assassinations about the land.
Kojiro has decided that he needs to become a strong oni, and that he needs to destroy the swordsman identity named Yagyu Munenori and become the man named Sasaki Kojiro. He intends to do this by fulfilling his last wishes as a swordsman and defeating the legendary Miyamoto Musashi. And so, he tells Musashi of a plot by Tenkai to hold Haruka, a member of the Tokugawa family, so that he hold the bakufu in his hands. It seems she is at the now-famous Ganryu Island, and that Kojiro has told Musashi this in hopes that he would come for their duel.
In the end, Munenori realises his place as a swordsman when he is defeated by Musashi. He becomes a swordmaster for the Tokugawa forces.