Shuntaro Chishiya possesses light-colored, slightly messy hair often tucked behind his ears, marked by a distinctive mole under his left eye. He typically wears light-colored hoodies, jeans, and sneakers, though his appearance gradually darkens throughout events. Adaptations consistently depict him in white or neutral-toned outerwear, including hoodies and loose-fitting pants. Born to parents in the medical field, significant parental neglect defined Chishiya's childhood. His parents prioritized hospital careers over family, leading him to view their marriage as professional advancement, not emotional connection. This upbringing fostered profound emotional detachment and cynicism about human nature. Before entering the Borderlands, Chishiya pursued medicine—initially as a surgical intern, later adapted to a pediatric cardiovascular surgeon. His motivation stemmed from questioning whether he genuinely cared about human lives. In one version, he discarded a dying patient's testament letter without remorse. In another, hospital superiors forced him to prioritize a wealthy donor's grandson over his patient, Hayato, who died. This event solidified his belief in systemic injustice and human selfishness, prompting emotional disconnection. Within the Borderlands, Chishiya demonstrates exceptional analytical abilities, specializing in Diamond-suit games requiring logic and deduction. His first documented game was Six of Diamonds (blackjack), where he developed mathematical strategies, exposed cheaters, and manipulated opponents to survive. He later observed the Five of Spades (Tag) game from an elevated vantage point, deducing the safe zone while remaining detached. At the Beach community, Chishiya served as an executive while secretly conspiring with Hikari Kuina to steal collected playing cards. He manipulated Ryohei Arisu into attempting theft as a diversion, betraying him to militants to gain trust and locate the true card repository. This action nearly resulted in Arisu's death. Chishiya justified such manipulation as necessary for survival, stating humans prioritize safety regardless of others' suffering. During the Ten of Hearts (Witch Hunt) game at the Beach, Chishiya confronted Suguru Niragi on the rooftop. After psychological taunting, he scattered cards to distract Niragi and used a makeshift flamethrower to set him alight, preventing further sniper attacks. He subsequently abandoned Kuina to pursue independent objectives, though they later reunited. Later, Chishiya participated in the Jack of Hearts (Solitary Confinement) game, identifying the impostor through behavioral observation and forming temporary alliances. His most significant development occurred during the King of Diamonds (Balance Scale) game against Keiichi Kuzuryu. Philosophical discussions revealed parallels between Kuzuryu's struggle to assign human value and Chishiya's disillusionment with medical ethics. Kuzuryu's self-sacrifice prompted Chishiya to acknowledge envy of those capable of selflessness. This realization catalyzed a shift. He intervened in a confrontation between Niragi, Arisu, and Yuzuha Usagi, deliberately taking a bullet intended for Usagi—an act of protection contrasting his previous utilitarianism. While recovering, he reflected on his journey, expressing a desire to live differently upon returning to reality and acknowledging jealousy of others' capacity for honesty and sacrifice. Chishiya functions as a strategic observer, often positioning himself apart to analyze situations. He maintains calm under extreme pressure and employs psychological manipulation as a primary survival tool. Initially viewing human connections as transactional liabilities, his interactions with Kuzuryu, Arisu, and Usagi gradually challenged his belief in universal human selfishness. His character arc concludes with a conscious choice toward self-redefinition, moving from detached survivalism to engaged, albeit still developing, humanity.