Ayumi Matsuoka, a second-year Houshou Private High School student and softball team captain, balances athletic prowess with a steadfast moral compass, prioritizing collective safety and decisive crisis management. Her practical attire—a blue tracksuit with white stripes, white-and-blue sneakers, and a white headband—complements her sharp features: short brown hair, blue eyes, and fair skin.

Initially dismissive of Mutsumi Oribe’s quiet demeanor and perceived fragility, Ayumi gradually becomes her fiercest defender, clashing with adversaries like Atsushi Kamijo while championing Mutsumi’s survival tactics. Her protective nature extends to vulnerable peers, particularly Mami Miura, whom she shields from both physical dangers and manipulative classmates. This guardianship grows fraught when Mami, aware of Ayumi’s hidden attraction to women, manipulates her through unwelcome physical advances.

On the island, Ayumi’s ingenuity surfaces in foraging expeditions, tactical combat strategies against giant insects, and orchestrating high-stakes maneuvers—such as sabotaging electrical systems to defeat a colossal dobsonfly. Though her leadership shines during crises, she grapples with guilt over peers’ deaths, her confidence wavering despite outward resolve.

Her arc culminates in a final act of valor: intercepting a lethal ambush by firefly larvae to protect Mami. Mortally wounded and succumbing to disembowelment, her sacrifice cements her as a selfless pillar within the group. Mami’s subsequent grief underscores their unresolved emotional tension.

While Ayumi’s pre-crash life remains undefined beyond her academic and athletic roles, her post-disaster interactions reveal layered conflicts—between courage and self-doubt, loyalty to others and internal struggles with societal norms and her concealed sexuality.