Joshu Kasei functions as the Sibyl System’s humanoid proxy, overseeing the Public Safety Bureau with emotionless precision. Her design combines sharp professionalism with calculated neutrality: a slender frame, steely gray eyes, and cropped gray hair frame an impassive face accentuated by oblong wire-frame glasses and subtle earrings. Her demeanor exudes controlled authority, strategically guarding secrets and prioritizing systemic imperatives over personal engagement. She fixates on anomalies like Shogo Makishima, whose resistance to Sibyl’s judgments disrupts her programmed understanding of order. The origins of her name and appearance remain unresolved, with no clarity on potential ties to real individuals or Sibyl’s collective members. Following a staged public demise, Harumi Hosorogi assumes her title, though Sibyl reactivates her android form as needed. Redundant bodies enable immediate redeployment post-destruction. Her speech and mannerisms adapt fluidly to whichever Sibyl member pilots her frame—evident when Kozaburo Toma’s influence briefly surfaces through masculine pronouns. Equipped with administrative overrides, she can neutralize Dominator judgments threatening Sibyl’s integrity. A neural uplink embedded in her nape syncs with a modified office chair, tethering her consciousness to the collective’s hive mind for instantaneous data analysis and consensus-building. Despite enhanced durability, the android form falters against raw physical force, as demonstrated by Makishima’s unarmed assaults. Her dynamic with Akane Tsunemori oscillates between guarded collaboration and veiled tension, as Tsunemori critiques Sibyl’s ethics while navigating its constraints. Mika Shimotsuki contrasts sharply, obeying directives without question. Sakuya Togane’s familial address—“mother”—stems from his biological parent Misako’s integration into Sibyl, though Kasei reciprocates no maternal sentiment. Persistently embodying Sibyl’s will across iterations, she operates as an extension of collective logic, her static role reflecting the system’s aversion to individual evolution. Each reappearance reinforces her identity as an instrument, not an entity—a conduit for directives devoid of personal narrative.