Even though they never thought that Sano would come and fight again. Sanosuke and Kenshin decided to resume their fight near the river once and for all. Kenshin told Yahiko and Kaoru not go watch him fight, but they still came.
Evening came and the battle begins, even though Sanosuke is good in maneuvering the Zanbatou it's still no match against Kenshin's speed. However because of Sano's strong will, he still remained standing receiving Kenshin's blows. His determination to defeat Kenshin is the only thing in his mind after all Kenshin worked for the Ishin Shishi, the same people that betrayed the Sekihoutai.
10 years ago, Captain Sagara lead the Sekihoutai group and Sano greatly admired and respect him because of his optimistic vision to make the country peaceful and a prosperous country to live in. Sano even adopted the Captain's last name as his own. After the Sekihoutai successfully won the battles, the government sensing that they couldn't keep the promise they made to the people. They told the people that the Sekihoutai are the traitors and the ones who are telling the false promises. They ambushed the Sekihoutai's hideout and executed the entire group. Sagara Souzou managed to escape with Sano. He threw Sano into the river before he was gunned down. Sano managed to escaped safely, much to his dismay when Captain Sagara's head was displayed in the town square labeling him as traitor.
Kenshin explained to Sano that he could not honor his Captain by causing violence but rather by ensuring peace. Gohei, seeing that his plans screwed up again, he decided to use gun instead (well, it's about time :P). But with both Kenshin and Sano, he was beaten to pulp again.
Sometime later they meet Sano again, and he kinda bragged that he's not quite injured. So Kaoru and Yahiko poked his injuries to prove if he doesn't felt the pain until he admits it.