In 2019, an uprising in the USA followed by a global nuclear war decimated humanity in a catastrophe known as "The Maelström." Half a century later, the World Health Organization (WHO) has gradually absorbed global political power to preserve humankind, completely redefining society: people are now treated as public resources and guaranteed a happier life. Advanced medicine, nanomachine technology, and augmented reality support this intensified focus on human health. Overwhelmed by the excessive kindness of Japanese society, high school student Miach Mihie decides to reject the societal values she finds dehumanizing before the health implant surveillance system WatchMe activates on her 18th birthday. Miach plans to commit suicide with two friends, Tuan Kirie and Cian Reikadou. However, Cian breaks the pact, disagreeing with Miach's intentions, which allows Tuan to survive her suicide attempt, whereas Miach is declared dead. Thirteen years later, Tuan, now a senior inspector for Helix—a WHO-affiliated organization monitoring military conflicts—is sent back to Japan after senior Helix inspector Oscar Stauffenberg discovers her drug smuggling activities in the Niger warzone. On her first day back in the country she tried to flee, thousands of people commit suicide simultaneously. Tuan is tasked with investigating this wave of mass suicides and exposing the terrorist organization responsible for the unprecedented attack.