Mirai Kuriyama is the last survivor of an almost extinct lineage of Spirit World Warriors, uniquely capable of manipulating her own blood—an ability deemed heretical by other clans. This power allows her to form weapons like swords or shields and emit corrosive sprays, but causes severe anemia with overuse. It necessitates wearing a sealing ring on her pinky finger and isolates her. A self-inflicted wound on her right arm or palm, hidden under bandages and often beneath her pink cardigan, provides quick blood access.

Orphaned and adopted by the Inami family, her powers led to isolation, broken only by genuine friendship with Yui Inami. Tragically, Mirai was forced to kill Yui in self-defense when the Hollow Shadow youmu possessed her friend. This act burdened Mirai with deep guilt and trauma. The Inami family sought vengeance, especially Yui's younger sister Sakura, but Izumi Nase intervened, protecting Mirai. Izumi believed Mirai's power could eliminate Akihito Kanbara, a half-youmu seen as a threat to Nagatsuki City.

Mirai's story starts as she contemplates suicide on a school rooftop, stopped by Akihito. Mistaking him for a youmu, she stabs him with a blood sword, discovering his immortality. She repeatedly attacks him for combat practice, seeking to overcome her paralyzing fear of killing youmu stemming from Yui's death. Financial hardship compounds her struggles, as her revoked Spirit World Warrior license prevents income from youmu extermination. Alternative livelihoods, like blogging about bonsai cultivation, meet online ridicule.

Akihito's unwavering support helps her confront her fears. Their bond strengthens during the Hollow Shadow incident, where Mirai disobeys orders to face the youmu alone. With Akihito's aid, she overcomes illusions of Yui and halts his berserk youmu transformation. This collaboration restores her confidence, though her license remains suspended for a month. Akihito later secures her part-time work with his acquaintances, Mitsuki Nase and the Shindou sisters.

Mirai reconciles with Sakura Inami after defending her in battle. They share an apartment and develop a close friendship. However, the emergence of the Calm—a phenomenon weakening youmu—reveals Akihito harbors "Beyond the Boundary," an ultra-powerful youmu. To save him, Mirai extracts the entity using all her blood, sacrificing her life. Akihito later enters a pocket dimension to help her spirit defeat it. Before vanishing, she confesses her love for him. Her physical form dissipates, but she miraculously reappears on the school rooftop a year later, alive yet amnesiac, lacking memories of Akihito, her blood powers, or the battle. She resumes daily life with Sakura, though a mysterious shadow implies lingering supernatural ties.

Physically, Mirai is petite with light peach-colored bobbed hair, golden-amber eyes, and distinctive red-rimmed glasses. Her standard attire includes a school uniform with a pink cardigan, grey or black tights, and the golden sealing ring. She exhibits self-consciousness about her appearance, especially during discussions about body image.

Personality-wise, Mirai is introverted, socially awkward, and initially withdrawn, often muttering "How unpleasant" when agitated. She blends shyness (dandere) with occasional outward coldness masking underlying warmth (tsundere). Her combat movements show agility and swordsmanship knowledge, though early trauma limited practical experience. Persistent and resilient, she dislikes ridicule and evolves from a fearful novice into a determined warrior. Her hobbies include sweets, high-calorie snacks, and bonsai care, though she struggles with cooking.