After a war that nearly destroyed Japan fifty years ago, the society has rebuilt around a centralized network called Sound Health Everlasting Long Life (SHELL). This advanced system helps guarantee that everyone is free of disease, using nanomachines and medical research. However, people must work 19 hours a day in exchange. An uncommon incident known as 'Human Lost' happens when someone disconnects from the SHELL system. They become monsters known as 'Lost' that must be destroyed to prevent society from collapsing. In this culture where pain and death are no longer a concern, an increase in antisocial behavior has emerged. Takeichi, a factory worker, intends to protest against his inhumane living conditions by besieging the Ministry of Interior. He convinces his painter friend, Youzou Ooba, to join him. Nevertheless, their suicide mission goes awry, resulting in Takeichi's body being beyond repair and him turning into a Lost. Youzou follows suit. In the chaos that ensues, member of the dispatch team, Yoshiko Hiiragi, discovers that Youzou possesses a unique ability to transform back into a human. As the third person to survive after becoming a Lost, Youzou helps Yoshiko investigate recent outbursts of the Human Lost phenomenon. These episodes could bring society's last chance for rebirth.