In a near-future society, the practice known as Kōka has become the norm: human brains are transferred into mechanical crab-like vessels, granting extended lifespans and a second life. High school girl Makoto lives uneasily amid this reality, unable to accept the widespread transformation that everyone around her embraces as inevitable. Her own father has undergone Kōka, and she tries to maintain a normal family life with his mechanical body. One day, a mysterious woman appears before Makoto and delivers a shocking declaration: the brain inside her father's machine is not his original mind but an artificial intelligence substitute. The woman claims she is part of a resistance movement opposing Kōka and that she has come to return Makoto's father's real brain to its proper vessel. Skeptical yet driven by growing doubts, Makoto decides to follow her. This decision shatters her mundane existence and pulls her into a hidden conflict between those who enforce Kōka and those who fight to reclaim humanity's organic future. As Makoto digs deeper, she learns that the deception goes far beyond her father alone. Alongside Shin, a young man who lost his original body to Kōka and now seeks to recover it, Makoto confronts the director of the Kōka Technology Research Institute. The director goads them with an unexpected challenge: if they want real change, they must bring down a specific powerful figure. Meanwhile, public sentiment against Kōka begins to quietly build. The story escalates into a battle action narrative that questions the nature of identity, the value of human potential, and what it truly means to be human in a world where minds and machines have become interchangeable.