Sojiro Seta is Makoto shishio's best man in the Juppongatana. Because of being abused by his siblings as a child Sojiro had become emotionless. He lived by the law "if you're weak you die, if you're strong you live" after meeting Makoto Shishio and working for him.
In episode 31 of the english dub from Sony Pictures from the mid 90s, Sojiro is voiced by Matthew K. Miller, but Mona Marshall took over the role of Sojiro for the rest of the series for unknown reasons.
When Mediablaster's purchased the license to Rurouni Kenshin, a new english dub was made using Bang Zoom! From episodes 31-47 Tara Jayne voiced Sojiro, but was not available for a few episodes so Lynn Fischer filled in episodes 50 and 51 and Melissa Fahn in episodes 54-56