Izumi Makihara, a childhood friend bound in a close triad with Yuu and Hime, shares a history steeped in unspoken romantic tension with Yuu. Her mysterious death two years before the main narrative leaves Yuu socially ostracized and spiraling into depression, while her consciousness imprints onto Eim during her final moments through Satori’s mind-reading abilities. This fusion transfers Izumi’s memories, emotions, and a soul fragment into Eim’s psyche, granting Eim control over two Ayakashi—including Satori, once Izumi’s own. The unresolved truth of her demise, compounded by Yuu’s misplaced guilt, fuels central conflicts and character drives.

Izumi’s psyche lingers within Eim, surfacing intermittently to influence decisions and relationships, weaving psychological tension into Eim’s journey. Yuu’s childhood vow to protect Izumi and Hime anchors his motivations, merging duty with grief as he navigates her absence.

A pivotal childhood encounter with parasitic "snowflakes" imbued with Ayakashi shapes the trio’s destiny, awakening supernatural abilities in Yuu and Hime. Izumi’s absence fractures their dynamic, her memory propelling Yuu’s growth and eventual clash with the broader Ayakashi conflict. Subtle resemblances between Izumi and figures like Orie Natsuhara hint at her enduring influence, though these ties remain indirect echoes of her legacy rather than explicit links to her past.