Return to Kyoto
After the final decisive Battle of Toba-Fushimi, where the imperial forces eventually won over those of the shogunate, Himura Battousai took up the reversed-edge sword and began his ten years of wandering with the oath of never taking life again. He had given up the way of the sword as penance for his murder of Tomoe, and of all that he had killed before. Nevertheless, it appeared that Kenshin's heart remained confused and uncertain, because even though he had given up the name of "hitokiri," he still had not found a way to atone for all his crimes. Most importantly, the assassin still lurked in a corner of his heart, and he could (and would) be pushed toward murder again.
During the course of his wandering, he met Kamiya Kaoru in Tokyo, and due to circumstances found himself staying in her kenjutsu dojo. While there, he gathered many friends and admirers, most of whom he saved in one way or another, using his skills with the sword. Though he stuck to his vow never to kill, his will was sorely tested twice. Once, when Kaoru's life was threatened by an assassin, Udou Jineh, and it seemed murdering him was the only solution. Then, when a former Shinsengumi, Saitou Hajime, turned up and challenged him after inflicting injuries on Sanosuke. Both times, Kenshin reverted to Hitokiri Battousai mode, fully intent on killing them. Both times he was saved from taking the plunge. Still, it was clear that Kenshin's vow did not hold him as tightly as he wished. Even though he loved Tomoe and repented sincerely, I believe it was easy for him to backslide into hitokiri mode because he still did not fully understand the value of life. Also, his compartmentalization of himself into Battousai-the-killer and Kenshin-the-wanderer also weakened him in a way, because deep down he felt that all his strength was in Battousai, that forbidding himself from taking lives weakened him. In Kenshin's own mind, Kenshin was infinitely inferior to Battousai in terms of skill and strength. (If you watch Heroes, think Niki and Jessica Sanders, living in the same body.) This was why, in moments when he was justifiably pissed, his pupils dilated and his brows drew down -- sure signs of a Battousai explosion. These "lapses" seldom lasted long, but the fact they occured at all several times during the series is a dead giveaway that Kenshin is not completely in control of his monsters.
He was further put to the test when he was requested by the government to find and defeat the former successor to the "hitokiri" title: Shishio Makoto. Shishio was planning a bloody revolt to overturn the Meiji government and establish his ideal country where the strong would rule over the weak with an iron fist. The only way to stop Shishio was to kill him, apparently. Obviously, the government had already tried, going so far as to burn him. Thus, Kenshin was faced with a grave dilemma. The future of the Japan that he had helped to build was in peril, but if he should break his vow -- even for the noblest of reasons -- he feared he would lose his sanity. Even worse, Shishio was the complete opposite of Kenshin, who saw as fodder the people Kenshin wanted to protect.
In the end, Kenshin returned to Kyoto to face Shishio, with his heart uncertain and his training incomplete, without knowing whether he could kill again.