"Tenka Hyakken" is set in a world where historical Japanese swords, known as katana, are personified as beautiful women called "Tsukumogami." These beings are tasked with protecting the world from malevolent spirits and preserving peace. The story centers around a young girl named Mei, who becomes the master of these sword spirits after inheriting a mysterious mansion called the "Tenka Hyakken." The mansion serves as a sanctuary for these Tsukumogami, who pledge their loyalty to Mei and assist her in combating supernatural threats.

The narrative unfolds as Mei learns to navigate her new role as a master while forming bonds with the sword spirits. Each Tsukumogami embodies the traits and history of their respective swords, with personalities ranging from stoic and disciplined to playful and mischievous. Key characters include Raikiri, a powerful and composed spirit representing a legendary sword, and Hizamaru, a cheerful and energetic spirit who often lightens the mood. Together, they face various challenges, including battling evil spirits, uncovering the mysteries of the mansion, and confronting their own pasts.

As the story progresses, Mei and her companions uncover deeper secrets about the origins of the Tsukumogami and the true purpose of the Tenka Hyakken mansion. The series blends action, fantasy, and historical elements, with a focus on the relationships between Mei and the sword spirits. The episodic structure allows for exploration of individual characters' backstories, while an overarching plot ties their journeys together. Themes of loyalty, duty, and the preservation of history are woven throughout the narrative, creating a balance between lighthearted moments and more serious, introspective arcs.