While strolling through the streets of Tokyo, Linn Suzuki spots a peculiar device protruding from the pavement. Suddenly, she is attacked by thugs and rescued by a beautiful stranger who defeats them all. It appears that young Linn has escaped Deep Kyoto from her cruel mistress and traveled to Edo, hoping to locate her long-lost brother, who was last seen working for the Kuon Detective Agency. By coincidence, this stranger turns out to be Miho Kuon, who allows Linn to stay with her (nicknaming her Kotetsu, or Little Tetsu, after her brother, Tetsujin). However, a mysterious organization known as the Syndicate is hunting Miho, and Linn is now caught up in the middle of it all.