Mirai is depicted as a petite girl with chin-length, wavy peach-colored hair styled in a bob, and golden eyes with shades of amber and brown.

Her usual attire consists of her school uniform layered with a light pink cardigan and gray tights. The cardigan conceals a bandaged wound on her right arm, which she uses to quickly release blood for her ability depicted in the light novel as a gash on her forearm and in the anime as a small round wound on her palm. In the light novels, she also wears bracelets to secure the bandages, and she constantly wears a simple golden ring on her pinky finger, which functions as a seal for her blood-manipulation powers.

During the summer, Mirai replaces her cardigan with a sleeveless sweater of the same style, worn over her summer uniform.

Her most recognizable accessory is her pair of thick, round, red-rimmed glasses, which she wears at all times. Although she briefly uses square black glasses, she quickly returns to her signature red pair.

It is later noted that Mirai closely resembles her mother in appearance, differing mainly in hair color and hairstyle.

Mirai is introverted, clumsy, and socially awkward, often blending into the background at school. She struggles with everyday life, having to support herself financially while initially being too fearful of confronting Youmu to earn income as a Spirit World Warrior, a profession that most warriors embrace. Her fear and lack of confidence also limit her combat experience, though she demonstrates a degree of fighting knowledge. Over time, through her interactions with others, Mirai gradually overcomes her insecurities, gaining confidence and eventually becoming a capable and experienced warrior.

A notable quirk of Mirai’s character is her frequent use of the phrase “How unpleasant!” (不愉快です！, Fuyukai desu!) when irritated or flustered. She is also poor at lying, as those around her particularly Akihito Kanbara quickly notice her habit of cleaning her glasses and avoiding eye contact when attempting deception.

Her personality aligns with traits often associated with dandere characters, though she occasionally exhibits tsundere-like tendencies. Despite her reserved nature, she is persistent when determined and dislikes being ridiculed. She is also self-conscious about her appearance, as seen when she reacts to conversations comparing physical traits, such as breast size, among her peers. Although she tends to avoid social interaction, Mirai’s bonds with those around her gradually help her emerge from her isolation.

Mirai is the last surviving member of a Spirit World Warrior clan known for the rare ability to manipulate blood, shaping it into weapons or unleashing it as a corrosive spray. Following the destruction of her clan, she was adopted by the Inami family, though she remained largely isolated because of the stigma attached to her powers.

Despite this treatment, Yui Inami, the family’s middle daughter, formed a bond with Mirai and became her closest friend. In the anime adaptation, Yui’s younger sister, Sakura, also shared a friendship with Mirai. Tragedy struck when the Hollow Shadow, a powerful Youmu, possessed Yui’s body. Forced into an impossible situation, Mirai killed Yui to save herself, an act that haunted her with deep regret. The Inami family, particularly Sakura, harbored resentment toward her for Yui’s death and sought retribution.

Before they could act, Mirai was taken in by Izumi Nase, head of the Nase family. Izumi believed that Mirai’s unique abilities might one day prove strong enough to eliminate Akihito Kanbara, a half-Youmu whom she considered a threat to Nagatsuki City.

Hemokinesis
As a descendant of a cursed bloodline, Mirai possesses the rare ability to manipulate her own blood. She most commonly shapes and solidifies it into weapons such as swords or shields. However, this ability is limited by her natural blood volume, preventing her from creating constructs larger than herself.

Acidic Blood
Mirai’s blood has corrosive properties, allowing her to burn or dissolve enemies. She can utilize this by spraying her blood outward or injecting it directly into opponents.

Swordsmanship
Mirai demonstrates a refined and elegant style of swordsmanship, using her blood-forged blade both defensively and offensively. She is capable of deflecting attacks while simultaneously countering with precision strikes.

Enhanced Agility
In combat, Mirai displays heightened dexterity, reflexes, and mobility. She is able to dodge attacks with ease and leap great distances without sustaining injury, feats beyond the ability of ordinary humans.

Darker Form
In Beyond the Boundary Movie: I’ll Be Here, Mirai becomes possessed by Miroku Fujima’s Youmu, causing her hair to turn black and her demeanor to shift into a darker personality. This transformation grants her enhanced power but inflicts severe chest pain as a side effect.

• Shadow Tendrils: In this form, Mirai can manifest tendrils of dark energy from her back, one of which bears a face at its tip.
• Pyrokinesis: She can generate and manipulate fire, either releasing it from the tendril’s face or channeling it through her sword. This ability allows her to amplify her attacks, such as destroying a Glaciate Barrier with a single strike.

Akihito Kanbara
Mirai first encounters Akihito on the school rooftop, where she impulsively stabs him, only to discover his immortality. She continues to attack him for practice, which gradually leads to a friendship. Akihito plays a key role in helping Mirai confront her fear of Youmu, and although she frequently calls him “unpleasant,” she comes to deeply care for him. In the series finale, when Mirai faces disappearance, she thanks Akihito for allowing her to meet him and confesses that she fell in love with him. Their bond is reaffirmed in Beyond the Boundary Movie: I’ll Be Here – Future, where they promise to stay by each other’s side and ultimately confess their mutual feelings.

Sakura Inami
After the death of her sister Yui, who was killed by Mirai when possessed by the Hollow Shadow, Sakura initially seeks revenge and hunts Mirai down. Following their battle, Sakura recognizes Mirai’s sincerity and ceases her hostility, eventually becoming her friend and roommate. She later demonstrates strong concern for Mirai, shown when she panics at her disappearance and lashes out at Akihito for withholding answers.

Mitsuki Nase
Mirai is introduced to Mitsuki through Akihito. While Mitsuki is initially cautious around her, the two gradually develop a friendship. Mitsuki occasionally engages in casual conversations with Mirai, and their relationship strengthens over time. Mitsuki also provides Akihito with crucial information about Mirai’s past, which becomes a pivotal element of the story.

The given name Mirai (未来) translates to “future.” Her surname Kuriyama (栗山) is composed of kuri (栗), meaning “chestnut,” and yama (山), meaning “mountain” or “hill.”