Yui Inami, eldest daughter of the Inami family and a Spirit World Warrior, maintained a close friendship with Mirai Kuriyama, whom the clan had adopted. She possessed a hyper, happy personality and had a younger sister named Sakura. Within the light novels, Yui acted as a mentor to Mirai alongside Yuuto Mashiro, while the anime adaptation emphasized her role primarily as Mirai's close friend.

Yui's death forms a central part of her background. While possessed by the powerful youmu known as the Hollow Shadow, Mirai Kuriyama killed her out of fear. This act left Mirai deeply traumatized and regretful.

The aftermath profoundly shaped other characters. Yui's sister Sakura initially pursued Mirai seeking revenge, carrying deep resentment over the killing. Flashbacks reveal Sakura did not initially blame Mirai and even offered her food during Mirai's grief, though Sakura later developed envy toward Spirit World Warriors like her sister and Mirai. Conversely, Yui herself had harbored envy toward Sakura's ordinary life, as revealed in conversations between Mirai and Sakura.

Yui's legacy endures through Sakura, who eventually reconciles with Mirai and references their shared history involving Yui. Her death remains a catalyst for character motivations and relationships throughout the narrative.