Kei Karuizawa, a fashionable and influential student, is recognized for her blonde ponytail, purple eyes, and meticulous appearance, often accessorized with a blue ribbon. She maintains early social prominence through a relationship with class representative Yōsuke Hirata, leveraging this connection to solidify her status and protect herself from bullying. Her outward persona projects confidence, vanity, and superficiality, frequently spending private points on clothing while displaying minimal academic motivation. She often studies little and prioritizes social activities, a habit stemming from extensive absences during middle school due to severe bullying. This past involved physical assaults, public humiliation, theft of belongings, and psychological torment, including forced confessions and destruction of her property. The bullying left a permanent scar below her left breast, which she hides obsessively, fearing it would repulse others and shatter her self-image. Beneath this facade, Kei harbors profound vulnerability and cynicism. She believes her peers tolerate her only due to her social standing, not genuine affection, leading her to adopt a parasitic survival strategy—attaching herself to powerful figures for protection. Her relationship with Hirata is transactional, serving as a shield. Her trauma manifests in skipping swim classes to avoid exposing her scar and intense anxiety about her past being exposed. Kei's development intensifies through interactions with Kiyotaka Ayanokōji. After Hirata fails to defend her against Class C bullies, she becomes Kiyotaka's informant, gradually developing trust as he protects her. Their dynamic evolves from mutual exploitation to genuine reliance, culminating in a romantic relationship where Kiyotaka accepts her scar and traumatic history without judgment. This acceptance allows her to lower her defensive barriers. A critical turning point occurs when Kiyotaka orchestrates a plan using Kei as bait to expose Kakeru Ryūen. Captured and tortured by Ryūen's group on a rooftop, she endures psychological and physical abuse, including water dousing, without revealing Kiyotaka's role. This defiance, driven by a desire to protect him and reclaim self-worth, showcases her latent resilience. Ryūen later acknowledges her mental fortitude, and Kiyotaka revises his view of her, vowing to safeguard her. Post-trauma, Kei exhibits significant growth: she abandons her parasitic mindset, prioritizes genuine connections, and demonstrates loyalty. She supports classmates like Maya Satō in romantic pursuits despite conflicting feelings, reconciles with peers during class exams, and expresses concern for Suzune Horikita during the sports festival, empathizing with her isolation. Her relationship with Kiyotaka stabilizes her, reducing flirtatious tendencies and fostering emotional openness, though she retains playful jealousy and occasional vanity. Kei's self-awareness remains central; she acknowledges her flaws and limitations, often reflecting on her reluctance to change. Her journey culminates in a willingness to sacrifice herself for others' well-being, particularly Kiyotaka's, symbolizing her transition from self-preservation to selfless devotion.