Mutsumi Oribe, a fair-skinned teenager with almond-shaped brown eyes and long, casually kept brown hair cascading to her lower back, dresses in a camouflage jacket, white undershirt, blue skirt, black stockings, and hiking boots, topped with a brown Stetson. Her weathered blue-and-white backpack, "Gomaotto," carries survival tools and insect specimens. Later iterations soften her look with a plain green jacket and lengthened hair, hinting at subtle femininity.

Once a bullied introvert mocked as "Bug Girl," she found refuge in her bond with Chitose Naruse, her sole confidant. Childhood explorations with mentor Inaho Enoki sparked her entomology passion, transforming fear into scholarly curiosity—a foundation for her insect expertise and survival skills, later vital when stranded on a perilous, bug-ridden island.

Guilt over classmates’ deaths reshapes her into a resolute leader, though killing insects torments her. She devises tactical solutions: aerosol flamethrowers, terrain-based traps, and heartbeat-dampening strategies. Her defining choices include sacrificing a teacher to thwart a tick onslaught.

Relationships reveal depth: Chitose’s unspoken affection meets Mutsumi’s quiet reciprocation, while clashes with figures like Jinno Mirei expose her tendency to forgive despite betrayal. Her steadfast loyalty contrasts sharply with peers’ opportunism.

Spin-offs like *Kyomushi Sanmyaku* mirror her journey through Inaho Enoki’s parallel survival tales. Post-rescue sequels hint at her trauma and adaptive resilience, though specifics remain sparse.

Underestimation of her knowledge sometimes leads to fatal oversights, deepening her self-reproach. This tension cements her duality: a pragmatic intellect anchored in empathy, equally compelled to protect life and dissect its mechanics—even when facing hostile swarms.