Sara, designated HW-9, is a genetically engineered humanoid forged in a clandestine military initiative to produce living weapons. Her physiology grants extraordinary capabilities, including transformation into a glass-like form resistant to damage and reversion to human appearance, paired with an elevated internal heat signature. These traits originate from her role in the HW project, a counterpart to the BW series designed to induce transient glass transmutation in subjects before triggering combustion.

Discovered by the S&A Detective Agency during an operation, she struggles with fragmented memories, unable to recall her birth name or history. An agency intern, Manami, assigns her the provisional alias “Sara.” Her emergence draws relentless pursuit from her creators, intent on retrieving their experimental asset.

While sheltered by the detectives, Sara develops a fierce loyalty toward her protectors, her defensive instincts intensifying as she forges bonds with the group. This compulsion propels her to challenge threats endangering their safety. Fragmentary revelations hint at her escape from a lab, though her origins and life prior to experimentation stay obscured.

Her combat skills include near-invulnerability in glass form and the capacity to unleash concentrated destruction, though the precise workings of these powers remain undefined. Her narrative arc traces a journey from hunted fugitive to proactive ally, centering on resilience and self-determination as she resists recapture.

Interactions with detective Shu and agency members underscore her tentative assimilation into a surrogate family. While her history as a military asset and test subject forms the core of her identity, the specifics of her creation and trauma remain veiled, anchoring her in a present defined by defiance and evolving alliances.