As Linn Suzuki roams the streets of Tokyo, she happens upon a peculiar contraption protruding from the sidewalk. Suddenly, a gang of toughs ambush her, but a stunning savior comes to her aid, expertly defeating the assailants. Linn navigated her way from the tyrannical grip of her mistress in Deep Kyoto, with the intention of locating her long-lost sibling, employed by the esteemed Kuon Detective Agency in Edo. Bizarrely, her savior is none other than Miho Kuon, who welcomes Linn to stay with her, fondly naming her Kotetsu, which means Little Tetsu, reminiscent of her lost sibling Tetsujin. Coincidentally, the Syndicate, a dubious organization, is targeting Miho, leaving Linn entangled in the chaos.