TV-Series
Description
Izumi Nase is the former head of the prestigious Nase Clan, Spirit World Warriors dedicated to maintaining balance between humans and supernatural youmu. She serves as the primary mentor to her younger siblings, Hiroomi and Mitsuki Nase, guiding them after their parents' absence. Her strict lessons about the sacrifices demanded of their duty profoundly shaped Mitsuki's worldview.

Izumi possesses a tall stature (170 cm), short black hair typically worn down, distinctive purple eyes, and a small beauty mark below the left corner of her mouth. Her practical attire often consists of shorts and long-sleeved shirts, accessorized with two necklaces—one featuring a small fish, another with red and green jewels—and a bracelet on her right wrist, conveying an overall impression of elegance and a motherly aura.

Her personality blends a formal, duty-bound demeanor with blunt honesty, often delivering frank remarks while maintaining a kind expression. As clan head, she prioritized the Nase family's responsibilities above personal relationships, employing strategic pragmatism against threats. This included authorizing observation of the dangerous Hollow Shadow youmu and later orchestrating plans to eliminate Akihito Kanbara due to the catastrophic "Beyond the Boundary" youmu within him. Her intense sense of duty and belief in preemptive threat removal led to morally ambiguous decisions, such as manipulating Mirai Kuriyama into self-sacrifice.

Izumi is an exceptionally skilled Spirit World Warrior. Her signature ability is "Glaciate Barriers," allowing her to sink targets into a dormant, limbo-like state of consciousness. She wields a unique double-bladed naginata that can separate into a three-section chain-linked staff, demonstrating mastery of dual-wielding and tactical combat analysis.

Her background reveals complexities. Years prior, she temporarily left the clan but returned to guide her siblings. During this period, she tasked Hiroomi with monitoring or eliminating Akihito and clashed with Spirit World Warrior Society member Miroku Fujima over their conflicting interests in Akihito, resulting in a stalemate that foreshadowed future conflicts. She had previously tracked the Kuriyama bloodline, noting its potential to suppress Akihito's youmu side, and identified Mirai as its last survivor.

A pivotal revelation occurs when Miroku exposes Izumi's secret: she harbors a youmu inside her body, a condition she accepted to protect her family and allies. Witnessed by Hiroomi, this disclosure shattered their relationship. Facing rejection and the youmu's growing influence, Izumi relinquished her position as clan head and exiled herself.

In the film "Mirai-hen," Izumi reappears as an antagonist under near-total control of the internal youmu. She dons a black bodysuit and wields her naginata against Hiroomi and Akihito, questioning Mirai about her past. It is revealed she absorbed this youmu from Miroku as a protective measure. During the climax, Hiroomi aids her in overcoming the youmu's influence. Her status regarding leadership of the Nase Clan post-recovery remains unspecified.

Her name "Izumi" (泉) means "fountain" or "spring," while "Nase" (名瀬) combines "reputation" and "rapids," interpreted as "renowned position," reflecting her clan's standing among Spirit World Warriors.