Sayaka Koyanagi is a black-haired girl with bra-length hair cut into square bangs and piercing blue eyes. Her attire—a swimsuit top, short pants, long gloves, and a collar marked with a plus symbol—contrasts with the anonymity of the hockey mask she dons during missions. As a leader, she assembles Collectors to amass 100 coins, determined to dismantle the alien-orchestrated "game" that trades coins for supernatural abilities. Scarred by betrayal, her past unravels through a clandestine romance with a female teacher, who withdrew from their relationship over ethical doubts. When a confidant exposed their secret, triggering the teacher’s suicide, Sayaka’s trust shattered. This trauma birthed her obsession with a power to enforce silence. Her ability conjures a choker woven from her own hair, which melds invisibly into the wearer’s skin. The collar tightens lethally if its bearer betrays group secrets, reacting to disloyalty with fatal precision. Guiding her Collectors, Sayaka champions evasion over combat, openly acknowledging their vulnerability. Her pragmatism carries risks: a mission deploying toxic oleander smoke spiraled into unintended devastation, forcing her to confront the ethical toll of her strategies. Alliances within her group hinge on coerced loyalty, exemplified by Claire Aoki, bound by the choker’s threat. Claire’s sister, Elena, shares a history with Sayaka from their school days—a thread linking past and present. Rooted in her surname, meaning "small willow" and tied to eastern Japanese heritage, Sayaka’s moral compass tilts toward noble ends. Yet her fractured psyche and ruthless methods paint a layered portrait of a leader navigating desperation, idealism, and the unforgiving calculus of survival.