Hime Yakushiji is Yuu's childhood friend, classmate, and neighbor, recognizable by her long pink hair styled in twin tails and blue eyes. An active and emotionally expressive member of her school's field hockey club, she enjoys popularity among both male and female students, though she sometimes displays a nosy tendency involving herself in others' affairs.

Hime harbors romantic feelings for Yuu, despite her awareness of his past affection for their mutual childhood friend Izumi. She consistently remains by his side. During Ayakashi conflicts, she becomes capable of perceiving the supernatural parasitic entities known as Ayakashi, which grant powers at a physical and mental cost. Her connection to this hidden world deepens, culminating in the revelation that she herself is an Ayakashi user.

A core element of her relationship with Yuu stems from his childhood promise to protect both Hime and Izumi. Yuu continues to honor this promise, though he occasionally maintains emotional distance from her. In the sequel timeline, Hime's familial connections expand with the introduction of her cousin, Kikuri Shirakami, the successor of the Shirakami family with abilities to seal and control Ayakashi; however, no direct interactions or relationship developments between Hime and Kikuri are detailed.

Hime faces danger, including assault, during the Ayakashi conflicts. Her character evolves from a primarily supportive childhood friend role to a more involved participant in the supernatural struggles surrounding Yuu and the other Ayakashi users.