Kaori, a pragmatic yet emotionally vulnerable college student, vacations in Okinawa with friends Erika and Aki to celebrate their impending graduation. Engaged to Tadashi, a Tokyo-based sound technician, her resolve to shield loved ones intensifies when fish-like creatures with mechanical legs trigger chaos, severing contact with Tadashi. Driven by their bond, she journeys to the mainland amid a spreading crisis, partnering with Shirakawa, a freelance videographer, to evade infected humans and mutated sea life.

Her resilience is tested as she witnesses grotesque viral transformations—organic hosts corrupted into mechanical hybrids—and confronts friends’ deteriorations, including Erika’s impulsivity and Aki’s simmering resentment. Moral quandaries arise over humanity’s worth in a collapsing world, compounded by her immunity to the virus, a divergence from the manga where Tadashi, now infected in the anime, shifts her role from protector to proactive survivor.

Navigating biomechanical horrors, her arc avoids tidy resolution, underscoring perseverance and the precariousness of human bonds against existential threats. Tensions among the group and her fraught decisions under duress crystallize her struggle to reconcile pragmatism with hope in a disintegrating reality.