Mayu, also known as Tomone, is a shinki who serves the god of learning, Tenjin. She was formerly one of Yato's shinki, given the name Tomone, which reflected his wish for a companion. As a former human who died against her will, she became a divine weapon bound to a god. Mayu has green eyes and black hair cut into a short bob with straight bangs, and she typically wears a white kimono with a red hakama. During her time with Yato, she wore a dark red kimono with light purple vertical stripes and a pink scarf.

Mayu is honest and blunt, unafraid to voice complaints when she dislikes a person or her circumstances. She has a strong sense of duty and holds herself and others to high standards of behavior as a shinki. At the same time, she possesses genuine compassion and sympathy for humans and fellow shinki who find themselves in difficult situations. Her personality reflects a practical, no-nonsense approach to the responsibilities of being a shinki, combined with underlying warmth.

Her primary motivation stems from a desire for stability and a sense of purpose. She left Yato because she could no longer tolerate living as the shinki of a shrine-less, wandering deity. Her departure was not born of malice but of a need for a more secure and structured existence, which she found under Tenjin. This decision highlights her pragmatic nature and her prioritization of her own well-being and spiritual health.

In the story, Mayu serves as a supporting character. She provides a perspective on the shinki experience, particularly regarding the challenges of serving a god who lacks a shrine and the importance of finding a proper place. She also acts as a foil to some of Yato's other shinki, demonstrating a path that prioritizes personal stability over emotional attachment.

Her key relationships include her former master Yato and her current master Tenjin. Her bond with Yato was severed when she left him, though she retains the memory of that time. With Tenjin, she has a more formal and stable relationship, serving him faithfully alongside his other shinki. She also interacts with other shinki and gods, often observing the dynamics of the supernatural world with a critical but not unkind eye.

Through her arc, Mayu demonstrates growth from a shinki who felt compelled to leave an unstable god to one who has found a secure and respectable role. She becomes more settled and confident in her position under Tenjin. Her development illustrates the theme that shinki can choose new paths and that seeking a better fit is a valid and sometimes necessary decision.

Her notable abilities include transforming into a weapon when her name is called. While under Yato, she took the form of a small dagger. After becoming Tenjin's shinki, her weapon form became a smoking pipe. This transformation is a fundamental ability shared by all shinki, and it allows her to serve her god in combat and spiritual tasks. Beyond her weapon form, she is knowledgeable about shinki conduct and the rules governing the divine world, reflecting her experience and seasoned perspective.