Mashiro Mito is the human incarnation of the Tayutai goddess Kikuramikami no Hime, sealed within a relic near Yachimata Shrine. Her accidental release occurs when Yuri Mito and his friends disturb the relic during spring break, shattering the seal and freeing many Tayutai, including the three powerful entities known as the Three Mightiest. She materializes as a young girl, dedicated to achieving mutual coexistence between humans and Tayutai.

Immediately upon release, Mashiro declares herself Yuri's wife and moves into Yachimata Shrine with him, believing marriage will foster harmony between their worlds. Profound affection for Yuri blossoms swiftly after being entrusted to his care. She earnestly strives to perform domestic duties like cooking and cleaning, though centuries of sealing leave her unfamiliar with modern technology and customs, resulting in comedic misunderstandings.

Mashiro maintains a calm, dignified, and optimistic demeanor, often speaking formally. She exhibits strong will and stubbornness, particularly concerning her ideals of coexistence. Despite a generally carefree nature, she adopts a strict, taskmaster attitude when training Yuri to harness his inherited spiritual powers to confront hostile Tayutai. Her own high-level spiritual powers are inherent to her status as a Tayutai deity.

Her appearance features distinct kemonomimi traits: long brown hair with spiky bangs, violet tareme-shaped eyes, pale skin, animal ears, and a furry tail. She typically wears traditional attire including kimonos, geta sandals, tabi socks, and a bell accessory.

After the events in Ashihara-chō involving subduing the Three Mightiest, Mashiro travels nationwide with Yuri, now her husband, to promote human-Tayutai harmony. They eventually settle in Takachiho City due to its high concentration of spiritual energy (Shinki), establishing a new Yachimata Shrine. There, she assumes a maternal role, raising Yuri's relative Kohaku while maintaining her mature and principled nature.

Mashiro's unwavering core motivation—achieving peaceful coexistence between humans and Tayutai—drives her actions across all media, including the original visual novel, its fandisc "It's Happy Days," the sequel "Tayutama 2: You're the Only One," its "After Stories," the anime adaptation, and the manga. Her character evolves from a mysterious supernatural entity into a devoted partner and caregiver, consistently advocating for understanding between species while adapting to human relationships and responsibilities.