Shinomori Aoshi (四乃森 蒼紫?), known in Western order as Aoshi Shinomori in the English version of the anime. Shinomori Aoshi was raised a ninja of the Oniwabanshū, who worked for the Shogunate government during the Edo period. He helped to raise Makimachi Misao from childhood as a member of the Oniwabanshū. At the suggestion of Kashiwazaki Nenji (better known as Okina), Shinomori was given the position of Okashira at the age of fifteen, in time for the Oniwabanshū to defend Edo Castle.
After the revolution, since a few members of the Oniwabanshū were unable to adapt to life in the Meiji era, Aoshi and these members worked for the corrupt, power-hungry business man, Takeda Kanryū instead. Aoshi's Subordinates included Beshimi, who specialised in darts and poison, Hyotoko, whose name literally means "Fire Man" and uses flint-and-steel teeth to breathe fire. Also were Han'nya, a skilled martial artist and deft ninjutsu practitioner, and Shikijo, a "muscle man".
Shinomori Aoshi is a very quiet, intelligent individual. He never speaks when unnecessary and he always thinks before he acts. He seems to be unemotional most of the time, earning him the nickname of "that gloomy jerk" from Myōjin Yahiko. Aoshi only smiles once in the manga (excluding the weird smirk when he sees Kenshin cut a lamp post in two) and around eight times in the anime. He doesn't show it, but he has a soft spot reserved for his friends and Makimachi Misao.
Aoshi appears to be very cool and level headed when we first see him, although we see glimpses of his obsession to defeat Kenshin in a few scenes. After Hannya, Shikijō, Beshimi, and Hyottoko die, and during the time Aoshi escapes from Kanryū's mansion, he seems to be in a shock, and his eyes have a shaded look, a conventional manga portrayal of depression, possession, or daydreaming. His intelligence and analytical skills are also well-honed evidenced from his display of narrowing the location of a mine below the water to a tenth of a degree and meter.
Aoshi is a grand master and okashira of the Oniwanbanshu shinobi. Aoshi's weapon of choice is a kodachi, a sword that is described in the series to act like a shield. He originally used only one of these short swords for defense outside of Kaiten Kenbu and relied mainly on kenpo for his offense, but later used a two-sworded style, employing a pair of the swords. When in their saya, they appear to be part of a single sheathed sword, one blade appearing to be the hilt, while the second blade is stationed opposite the first and blends in with the saya itself, giving it the impression of being a nodachi. A dangerous opponent, he uses his speed together with a mix of sword and hand-to-hand combat moves.
Onmyō Kōsa: (Shadow-Light Cross) Aoshi blocks an enemies striking weapon with one kodachi, then strikes it with the second kodachi, thrusting the first one through.
Jissen Kenbu: (Actual-Battle Sword-Dance) Combo attack using "Ryūsui no Ugoki" to flow around the enemy, confusing them. Aoshi will then strike from various points, slashing them with his kodachi, before deciding to end it with "Kaiten Kenbu". Before deciding to use a two kodachi style of fighting, this was Shinomori's final attack.
Kaiten Kenbu: ("Spiral Sword Dance" or "The Dance Of The Wheeling Sword") Aoshi claims to have used this attack to defeat "all who intruded upon Edo castle". It involves Aoshi rapidly spinning around three times, while holding the kodachi backhand, to slash the opponent thrice in an instant. Aoshi usually uses this attack after disorienting the opponent with Ryūsui no Ugoki.
Kaiten Kenbu Rokuren: ("Spinning-Heavenly Sword-Dance Six-Series" or "The Dance Of The Wheeling Sword Six Successions") This attack is Aoshi's ōugi. The attack involves Aoshi gripping his kodachi backhand, then slashing the opponent six times in rapid succession, from both sides (it relies on confusing the opponent on the direction from which each subsequent strike is going to come). It's basically Kaiten Kenbu but done with two kodachi.
Onmyō Hasshi: (Dusk to Dawn Strike) Aoshi throws both kodachi at the opponent, hitting the end of the first one with the second one for an extra boost. The second kodachi is hidden directly behind the first. So the opponent would only see one kodachi heading for them in their line of sight.
Gokō Jūji: (Yin-Yang Cross) Aoshi crosses the two kodachi and moves them outwards in a scissor-like cut.
Ryūsui no Ugoki: (Flowing-Water Movement) This is moving technique where Aoshi moves around silently, rapidly alternating between fast and slow movements and confusing the opponent due to the fluid motion & continuously changing speed. It can be beaten by watching for the moment the user attempts to strike.