, addressed as Sojiro Seta in the English anime, is a fictional character from the Rurouni Kenshin manga series created by Nobuhiro Watsuki. He is Shishio Makoto's 16-year-old right-hand man. Sà Âjirà  has been favorably popular with the Rurouni Kenshin reader base, placing high in several popularity polls.
Nobuhiro Watsuki has stated that the character design of Sà Âjirà  is loosely based on Okita Sà Âji, the captain of the first Squad of the Shinsengumi. The name Seta Sà Âjirà  originates from "Okita Sà Âjirà Â," the name Okita had in his early life. The specific personality model is from the Okita in Ryà Âtarà  Shiba's novel Shinsengumi Keppà «roku ("Record of Shinsengumi Bloodshed"); in that version Okita "lost an important part in his human heart," making him without emotions and "pretty scary." Watsuki reported that some fans did not like the fact that a character modeled on Okita is a villain; Watsuki argued that since Sà Âjirà  is based on the Shinsengumi Keppuroku Okita, the design "works well" and that Sà Âjirà  is "a strong antagonist." Watsuki felt that Sà Âjirà  was more difficult to draw than Watsuki initially anticipated, and that he only accomplished around one fourth of what he imagined the character would appear in his mind. Watsuki had no design model for Sà Âjirà Â; Watsuki envisioned Okita as having bangs (fringes), so to Watsuki it was no surprise that Sà Âjirà  also had bangs. Watsuki gave Sà Âjirà  a "slightly feminized air" so that Sà Âjirà Â's smile would "look good" on the character. In Volume 9 Watsuki stated that he wants to properly portray Sà Âjirà  since he is a popular character.
The fact that Sà Âjirà  has no emotions is also based on Shiba's version of Okita Sà Âji. Watsuki said that this concept became one of the most difficult aspects to reflect in the drawing. Okita died when he was young, but Watsuki decided not to kill Sà Âjirà  in the story in order to atone for the murders he committed, but instead start living on his own instead of having someone make his decisions for him. He hoped to draw him in more of the next chapters but soon thought that would not be possible.
Sà Âjirà  is Shishio's right-hand man, a young assassin trained by Shishio himself. Sà Âjirà  is known for his lack of kenki (offensive aura) in a fight, his apparent emotionless state reflected also in his sarcasm and polite manners with his smile hiding his true feelings. However, he does have a special relationship with Komagata Yumi, who functions as an older-sister figure towards him. Sà Âjirà  usually dresses up in a blue kimono with white handguards.
Born in Kanagawa Prefecture in September of the first year of Bunkyà « (1861), Sà Âjirà  is an illegitimate child who was badly mistreated by his father's family to the point of being beaten for faltering in his tasks. To build a tolerance to the beatings, Sà Âjirà  put on a smiling face as his tormenters decide to let him be. One night, at age six, Sà Âjirà  witnessed the recently scarred Shishio Makoto killing two police officers and was spared due to the criminal seeing the boy's smile. While secretly feeding Shishio and providing him with bandages, Sà Âjirà  takes the man's ideals to heart while receiving a wakizashi. When his family learned that he is harboring Shishio and decide to murder the child and pin the blame on the fugitive, Sà Âjirà  uses the wakizashi Shishio gave him to slaughter his family. Soon after, once Shishio's wounds are healed, Sà Âjirà  travels with him as his right hand and member of the Jupongatana.
Sà Âjirà  first appears in the storyline when he uses his superhuman speed to reach and assassinate government official à Âkubo Toshimichi, also killing the official's would-be samurai assassins who would historically take credit for à Âkubo's death nonetheless. Later, after Senkaku's defeat, Sà Âjirà  duels with Kenshin using Battà Âjutsu with the fight ending in a tie when their swords shattered. Sà Âjirà  is then assigned by Shishio to gather the Jupongatana located in the east side of Japan.
When Kenshin finally arrives at the Room of Reduced Space in Shishio's lair, he finds Sà Âjirà  waiting for him and at first has the upper hand due to his superior speed. But when the confrontation forces Sà Âjirà  to question Shishio's principles, his true emotions surface with allowing Kenshin now able to read his moves and defeat him. Despite his defeat, Sà Âjirà  informs Yumi of the key to Kenshin's ultimate attack while asking her to give Shishio the wakizashi that kept before leaving.
In the aftermath of Shishio's death, Sà Âjirà  becomes a wanderer to find his own truth and ideals. Five years later, he makes his way to Hokkaido where he is reunited with fellow Jupongatana member Yà «kyà «zan Anji, who was being escorted to Hakodate by Sugimura Yoshie (Nagakura Shinpachi), and joins them.
Sà Âjirà Â's apparent lack of emotion, his simple, cold-blooded mentality that , and his skills make him a formidable foe for Kenshin. As a master swordsman of his own style, Sà Âjirà Â's abilities have earned him the nickname of . His shukuchi utilizes such powerful speed that, to an observer, it appears that the distance between the two fighters has shrunk (hence the name shukuchi, which means "reduced earth").
During his fight with Kenshin, Sà Âjirà  continually states he's only moving "three steps below shukuchi" or "two steps below shukuchi." While moving at the speed his shukuchi utilizes, the only thing that can be seen is Sà Âjirà Â's footsteps ripping through the tatami mats. During "one step below shukuchi", he is able to attack from an omni-directional angle, utilizing not only horizontal but vertical space. While performing true shukuchi, he completely disappears and cannot be seen, even by Kenshin. Sà Âjirà  can dodge the , a move which apparently cannot be evaded even by Kenshin himself. Sà Âjirà  is also the first one ever to slash Kenshin in the back in the series.
Sà Âjirà  is also well versed in the Battà Âjutsu style like Kenshin, as is evident when he decides to use a stance similar to Kenshin's and when he destroys Kenshin's first sakabatà Â. Combining the true speed of shukuchi with the Battà Âjutsu, he has created his only named technique, , meaning "immediate killing by heaven's sword". It is named this because the speed behind the attack is so swift that the opponent not only dies before falling to the floor, but there isn't even time to experience pain. Judging by its appearance in the anime, it appears that the Shuntensatsu is very similar to Kenshin's Amakakeru Ryu no Hirameki, except that it uses speed rather than strength.
Ryunosuke Kamiki is cast as Sà Âjirà  in two live-action adaptations of the Kyoto arc: ' and '. He would later reprise his role in ' as an ally to Kenshin.
In ', Sà Âjirà  has become a wanderer to find his own truth and ideals. He makes his way to Hokkaido where he is reunited with fellow Jupongatana member Yà «kyà «zan Anji.
Daryl Surat of Otaku USA said that while Sà Âjirà  is a "kid," the character scored highly in popularity polls among readers because Sà Âjirà  always smiles despite the abuse inflicted upon him. Surat used Sà Âjirà  as an example for labeling Rurouni Kenshin what he calls "neo-shonen"; a work that appeals to both boys and girls. The inclusion of Seta Sojiro in The Final was praised for Ryunosuke Kamiki's performance as the character became an aid to Kenshin and wants to see his resolution to his life as a pacifist while also enjoying the bigger focus on Misao and Saito. The romance between Kenshin and Kaoru was criticized though as being underdeveloped.