Aoshi became the leader of the Oniwabanshu (The "Okashira") at the age of fifteen, when it was time to defend Edo castle. He was given the title due to Okina's suggestion. Shinomori raised Misao Makimichi, who became obsessed with him as she grew up. He always wanted to be the strongest of the Bakumatsu era, so he could prove to Kenshin, the Battousai, that he was beter than him once and for all.
Enter: the Okashira
Aoshi first appeared in the manga as a guardian of the crime lord, Takeda Kanryu, who made a living selling opium and making business on the black market.
The quarrel between the Kamiya style dojo and Takeda Kanryu started over a woman named Takani Megumi. She had bursted into a room full of gamblers (Sanosuke Sagara and Himura included) and asked for help from two men who came after her. Naturally Kenshin wouldn't refuse a cry for help. It didn't take Sanosuke long to figure out why she ran away from these men. She sold opium for a crime lord: Kanryu Takeda.
She stayed with the Kamiya dojo for a while and after a while she gave her story and told them about the group of Kanryu's body guards: the Oniwabanshu.
Kenshin and Aoshi (the leader of the Oniwabanshu) eventually fought after the rest of Aoshi's men(part of the Oniwabanshu) had been defeated by Kenshin and company. Kenshin and Aoshi fought for a while, and things looked bleak for Kenshin. Eventually Aoshi was struck in the throat with his own blade hilt and was forced to surrender. The battle would have ended honorably if Takeda hadn't come in with a Gatling gun that he had planned to finish them all off with. Aoshi survived multiple shots to the legs after each of his men had died to save him from the multiple shots that Takeda had loosed. The police arrive ready to take Aoshi and Kanryu only to find that Aoshi had already escaped.
The only one to find him was Kenshin
, who had arrived just in time to see Aoshi holding the severed heads of his comrades.
The Kyoto Arc
Aoshi then vows that he will be the greatest before disappearing into the night.
It is shown that Aoshi was asked to join the ranks of Shishio's men in his plot to take over Kyoto, but he refused the Four "monks" that asked him and killed them all with one blow, because of the disrespect they were showing by desecrating his friends graves. This is when he is shown to have mastered the Double-Kodachi (short sword) style.
Aoshi is a grand master and Okashira of the Oniwanbanshou shinobi. Aoshi's weapon of choice is a