Saviour
There are several interesting parallels between Himura Kenshin and Seta Soujirou, even more so than between Kenshin and Shishio, due to some very similar personal experiences.
Like Kenshin, Soujirou was orphaned at an early age. To make his situation even worse, his mother was only his father's mistress, and not his wife. He was sent to live with his father's legitimate son and his family, where he endured some pretty horrific abuse. Similarly, Kenshin lost his parents at the age of eight and was taken by a slave caravan. His life as a would-be slave was not likely to have been one full of rainbows and moonbeams, and though he may not have been treated quite as badly as Soujirou, it is doubtful that he was treated well by the slavers, apart from the three women who took care of him.
Most importantly, both Soujirou and Kenshin were saved from what may have been even worse fates by strong men when they were both about nine years old. Of course, the main difference is, Kenshin was saved by Hiko Seijuurou, whose greatest fault is perhaps his staggering narcissism, while Sou was "saved" by his fateful encounter with a murderous, psychopathic maniac with delusions of grandeur (also known as Shishio Makoto).
The nature of the instruction these two men also provided were vastly different. Hiko taught Kenshin the way of the sword so he could help the weak, while Shishio taught Sou how to take advantage of the weak (or worse, to prey on them).
I suppose some will say that it's not just a matter of who rescued whom, but also on the nature of the person himself, but Kenshin and Soujirou weren't that far apart in temperament as children. Kenshin, when the bandits who had killed his whole slave caravan had been slain, had buried them all. Soujirou, when given Shishio's wakizashi with his first lesson on the weak being the food of the strong, decided to return the sword because, knowing the pain of being slapped around, also realized the pain of being cut with a sword. Soujirou's character was naturally gentle, but it had been stamped out of him -- not just because of his relatives' abuse, but mostly because of Shishio's words. Nine-year-olds are easily impressed and influenced, after all, and given Soujirou's vulnerable situation, Shishio was able to very easily sway him into believing his philosophy. Even so, in his heart, Soujirou deeply regretted his first murder(s), a fact which would resurface years later.
The volume (16) which revealed Soujirou's past and the pivotal moment in which he turned to the "dark side" is one of my favorite volumes, and it is also one of the saddest. Every time I read Soujirou asking why Kenshin hadn't come along to save him when he needed saving, I find it heartbreaking. But there does one of their many differences become clear. Kenshin hadn't been looking for a saviour, but he had been saved. Soujirou had been waiting for one, and in the end, he never was. Even at the end of their battle, Soujirou was looking for a hero, in the person of Kenshin, who would tell him (decide for him) what path to take in life. Ultimately, as when Kenshin buried the hitokiri in him, Soujirou would have to learn to use his own strength to save himself. And so he decided to set off on his own ten-year journey, exactly as Kenshin and Shishio had, to find his own truth.
In a final twist, Kenshin himself became the saviour of a ten-year-old boy: Myoujin Yahiko. Yahiko seems to be developing talents (and a character) that may very well equal, or even surpass, Kenshin's. I find this pattern interesting.