Linn Suzuki, alias Kotetsu, fled her rural home to escape persecution by a cruel witch, seeking refuge in a metropolis. Her journey began upon discovering a dice on the ground, an event that led to a thug attack. Detective Miho Kuon rescued her, providing shelter and ongoing protection.

Kotetsu speaks with exaggerated eloquence and masters "kirohatchi," a swift sword draw technique vital in her battles. She confronts adversaries directly, including the seductive dryad Kagari. Her motivation stems from rural isolation and the quest to find her long-lost brother, Tetsujin, which drove her to the city.

Her complex relationship with Tatsuya Mikado, a shy and socially awkward love interest, involves mutual pining and notable age differences. Residing under Miho Kuon's guardianship, Kotetsu evades pursuit by a mysterious evil agency intent on her capture. Her alias originates from "Tetsujin Junior," a nickname from allies reflecting steel or sword craftsmanship. She continues navigating these personal challenges while evading the pursuing organization.