There's only one character stronger in Rurouni Kenshin than Kenshin himself and that's his master, Hiko Seijuro the 13th. Hiko is a giant, not unlike a huge black bear. With his long black hair and billowing white cape, he leaves an impression on all he meets. Hiko is a misanthrope who lives in the mountains above Kyoto to avoid contact with other people. He loves nothing more than drinking sake and doing pottery to pass the time.
In 1858, Hiko slaughtered a group of bandits who had raided a slave caravan and were about to kill a little boy with red hair and huge violet eyes. Unable to get the boy out of his mind, Hiko returned to the scene of the carnage a few days later to find that the child had buried all the dead. Moved by the boy's compassion, Hiko took the boy on as his apprentice and renamed him Kenshin or "Sword Heart".
For four years, Hiko trained Kenshin in Hiten Mitsurugi Ryu. However, things were brewing far away from Hiko and Kenshin's mountain home, in the capitol Kyoto. The Bakumatsu no Douran which had been raging since Kenshin's early childhood, grew more and more violent. Whenever Hiko and his deshi left the mountain, the red-haired youth saw suffering all around him. The suffering reminded him of the deaths he'd seen as a child.
Finally, at age 13 Kenshin confronted his shishou with his desire to help the nation's people. Hiko shot his plans down immediately, telling Kenshin that he should concentrate on his training rather than the outside world. Kenshin countered that Hiten Mitsurugi Ryu was meant to protect people from suffering and that this was the time to take up their swords.
Hiko warned Kenshin that the power of Hiten Mitsurugi Ryu would bring victory to whichever side they aided and change the course of history. Kenshin was adamant in his desire to fight and finally left the security of Hiko's mountain for the uncertainty of wartime Japan.
For the next four years, Hiko kept tabs on his baka deshi (idiot apprentice) from a distance and heard about his exploits first as a shadow hitokiri, then as a free striking swordsman. In 1868, after the battle of Toba Fushimi, news of Kenshin stopped cold and Hiko heard nothing more for a decade.
In May, 1878 Kenshin returned to Hiko to beg his old shishou to train him in Hiten Mitsurugi Ryu's ougi (final secret) so he would be strong enough to fight Shishio Makoto without reverting to his Battousai mindset and keep his non-killing vow.
Hiko rebuked Kenshin and told him the situation with Shishio was partially his fault because Kenshin's power had swayed the decisions of the Isshin Shishi and had caused them to put Shishio in place as a shadow assassin. Hiko was about to refuse to teach Kenshin the secret, when Yahiko, Misao and Kaoru came into the cabin and confronted him on Kenshin's behalf.
Kenshin's friends told Hiko that Kenshin had spent the last decade wandering through Japan, helping and protecting people. When Hiko heard that, he was relieved that Kenshin had at last internalized the values he'd tried to instill him all those years ago. With that in mind, Hiko agreed to teach Kenshin the secret. Thus began Hiko and Kenshin's second stint as shishou and deshi.