The Oniwabanshū were the protectors of Edo Castle during the Edo period.
In Rurouni Kenshin, they are introduced as Aoshi Shinomori, Han'nya, Shikijō, Hyottoko, and Beshimi. This group would later be known as the Tokyo Group. This group is one of two smaller factions which once comprised a single powerful clan of ninja. The other group from Aoi-Ya is comprised of Okina, Misao, Shiro, Okon, Kuro and Omasu are known as the Kyoto Group.
After the Bakumatsu, the Oniwabanshu was left leaderless and the mantle was offered to Okina but as he considered himself too old he offered the job to the much younger but highly skilled Aoshi this the Okashira/leader is currently Aoshi Shinomori who is also the youngest Okashira to have ever taken control of the group. When the Meji era came about of all of the Oniwabanshū members, only Aoshi received job offers from government agencies, such as the intelligence services of the Army of Japan and protection services of political leaders; Aoshi instead chose to be a hired guard as his comrades would be able to work with him.
While the goal of the Kyoto group was mainly to protect the people, Aoshi Shinomori wanted to become the strongest of the Bakumatsu and thus attempted to kill Kenshin, the Battousai simply to prove this, But this was clouded his judgement, and he was eventually redeemed thanks to Kenshin and the memory of his friends in the Kyoto arc.