Kagari Izuhira is a character who initially appears as a frail yet domineering figure, acting as a major obstacle to the friendship between Mato Kuroi and Yomi Takanashi. She is a childhood friend of Yomi, and their shared past is the foundation of her entire role in the story.

Her background reveals the source of her pain and possessiveness. As young children, Kagari and Yomi were inseparable, with Kagari being intensely devoted to Yomi. When Yomi had to move overseas with her family, a young Kagari chased after the departing car and was hit by a vehicle. Though doctors found no physical damage to her legs, the psychological trauma was so severe that she became unable to walk, spending her days in a wheelchair and largely confined to her home. This accident created a deep, unspoken guilt within Yomi, who felt responsible for Kagari's suffering.

Kagari's personality is defined by an extreme, possessive obsession with Yomi, which manifests as controlling and emotionally manipulative behavior. She forbids Yomi from making any other friends, declaring that Yomi belongs to her and must "take responsibility" for her condition. She has a childlike exterior, often appearing in a white sleeping gown with long, messy blonde hair and being very fond of macarons. However, this is a mask for a sharp, cruel, and manipulative nature. She is openly hostile to Mato Kuroi, viewing her as a threat who will take Yomi away. Her cruelty is passive-aggressive; she offers Mato "dirty-colored" macarons and speaks through her doll, Mary, to deliver hurtful messages. At her worst, she resorts to extreme measures to maintain control, such as carving a scar into her own chest or throwing herself down a flight of stairs, all while blaming Yomi.

Her primary motivation is the fear of abandonment, driving her to isolate Yomi completely to ensure she can never leave. This makes her the central antagonist in the early story, as her actions directly cause Yomi's growing emotional distress and transformation. Kagari's role is intrinsically tied to the show's concept of "other selves," as her counterpart in the psychological other world is a powerful, chariot-riding being named Chariot.

The key relationship in Kagari's life is, of course, with Yomi Takanashi. It is a toxic, codependent bond built on years of guilt and manipulation. Her secondary relationship is with Mato Kuroi, whom she initially despises as a rival for Yomi's affection. Minor relationships include the other girls at school she later befriends after her transformation.

Kagari undergoes a dramatic transformation following a climactic event: her other self, Chariot, is beheaded by Black Rock Shooter in the other world. The death of Chariot causes Kagari to lose the emotional pain and memories that had been weighing her down. She wakes up changed, suddenly able to walk and largely forgetting the intensity of her obsession with Yomi. This leads to a new phase in her development where she becomes a popular, academically successful student who excels at baking macarons, ironically the very thing she once hoarded. Her personality shifts to being more independent, and she even tells Yomi that she barely remembers their past, requesting to end their dependent friendship. However, when Chariot is later revived, some of her original feelings and memories return, allowing her to reconcile with Yomi and Mato and form a genuine, balanced friendship with them by the story's end.

While her personal, real-world abilities are not supernatural, she is highly intelligent and skilled in psychological manipulation. In the other world, her "other self" Chariot possesses significant combat abilities, including a massive spider-like wheel for mobility and a large wheel-shield that can fire steel needles, as well as the power to launch giant, crushing macaron projectiles.