Shinomori Aoishi: The One Who Lost His Way
Aoshi, fallen leader of the Oniwabanshuu, is like Kenshin minus a few complications, and put through the entire emotional spectrum in the space a few months. Kenshin's spiritual and psychological journey took over a decade. Aoshi, in a perfect demonstration of his burning need to be the best, one-ups him by doing it all in a year.
Aoshi started out with some admirable motives, namely the desire to prove his worth and the responsibility to take care of his team - the outcasts and misfits of the Oniwabanshuu. His obsession with being the strongest, however, totally warped his personality and blinded him to what was really important. Unfortunately, his Oniwabanshuu thought all too clearly, and didn't fail to remember what they were truly living and fighting for. The Oniwabanshuu ended up dying for Aoshi, and in his grief, Aoishi completely lost his mind. The deaths of his charges (for he was responsible for them, as their leader) left him with nothing but a taste for violence. He claimed to want to lay the name of "the strongest" at the Oniwabanshuu's graves, but what he really wanted was Kenshin's blood. It wasn't even revenge - he was perfectly aware of who was truly to blame. It was sheer craziness.
However, the story of Aoshi's redemption ties in closely to Kenshin's, for both of them ultimately changed for the sake of the happiness of a girl they cared for. Kenshin refused to kill Aoshi at Okina's request. I think that he did so not only because of his vow (of which he was having doubts he could keep, anyway), nor was it only because Misao would have been saddened, but because it would have been rather hypocritical of him, I think. When Okina said that the only way to put an end to Aoshi's violence was to kill him, Kenshin could not possibly have agreed. After all, as Hitokiri Battousai, he had been violence and death incarnate, and yet there he was: living and changed. In their final battle against each other, Kenshin forces Aoshi to recall his former self, and though they still carry on with the fight, they do so solely for the purpose of closure.
Aoshi is a leader of ninja, but unlike the others in the Oniwabanshuu, he relies more on his knowledge of kenjutsu than ninjutsu. Still, he is the most unconventional sword fighter in the extended Kenshin-gumi, using two swords and kodachi rather than the more traditional katana.
Aoshi is the series' resident poster boy for angst, doom, and gloom. I believe there's a sense of humor there, however. Buried somewhere under that white coat of his. Prolonged exposure to Misao may do just the trick.