Ruroni Kenshin is a fighting shounen from the '90's that is one of the best in its genre. It has a well-foreshadowed and complex plot, an interesting setting, and well fleshed-out cast, antagonists included. The thing in this regard is that the villains of the second arc are actually a mirror image of the heroes, at least for the most part. In this post, I wish to explain how precisely this is so.
Shishio: Being the most obvious foil, to the main character no less, he shares a similar past to him, also being a Battousai. Unlike Kenshin though, he refused to reveal his name to the public and thus being named a possible trouble by the government as he could easily expose their secrets with no repercussion to himself, was shot and burnt. He survived this however, and gathered a group of people to his side just a Kenshin did. His intention to overthrow the government is also a direct opposite to Kenshin's desire to retain it. His humorous personality is similar to Kenshin's comedic side.
Komagata Yumi: Being a parallel to Kaoru, she also has a similar hair color as her and shows a sisterly affection towards Sojiro much in the same way that Kaoru does to Yahiko. The two of them are also the main love interests to Shishio and Kenshin.
Yūkyūzan Anji: Being a foil to Sanasuke, he also has a tragic past involving the loss of those he loved which led him to bear a grudge against the current government. He also uses only his bare hands (and arms) in his fighting technique, being disinclined from swords much in the same way Sanasuke is after his fight with Kenshin. He even is the one to teach Sanasuke the technique, furthering the parallel all the more.
Uonuma Usui: A foil to Saito Hajime, he harbors as much of a grudge to Shishio as Saito does to Kenshin. Both this characters fight alongside those they bear a grudge to regardless. Both, however, are in truth past their grudge and do not actually wish to harm their respective opponents but are trying to push an ulterior motive. In the case of Saito, this is the testing of Kenshin's powers. In the case of Usui, this is to give the impression he still wants to kill Shishio. It is also worth noting that they are the most vile out of the supporting cast that either Kenshin or Shishio have, Saito being the only one willing to kill his opponents out of the former's group and, out of the latter's, Usui being the sole person to attempt to kill a child to get his way (an action Anji interrupts him in).
Sojiro Seta: He is the foil to Yahiko and is also the youngest in his group. His high power level is paralleled by the skill and fast learning capabilities of Yahiko and his repressed emotions can be likened to Yahiko's tough exterior being a front for his more emotional side. Both are like son figures for their respective leaders and were abused by irredeemable villains in their childhood. Both of them had their parents die when they were kids and both encountered their group leaders by accident. The real difference is that while Kenshin saved Yahiko, Sojiro was made to save himself by Shishio. Also, while the front Sojiro puts up is more playful, that of Yahiko is aggressive.
The rest of Shishio's team doesn't have a parallel as far as I can tell though it's worth noting how Shinomori Aoshi switched sides in the conflict, essentially being his own parallel, so to speak, on the two sides.
It is also worth noting that Kenshin, Sanasuke, and Saito all fought against their own foils at some point.
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