It is 2025. Five years have elapsed since the Tokyo Olympic Games were cancelled following deadly terrorist attacks. An international school operated by the United Nations now occupies the former Olympic site on the edge of Tokyo Bay. Among the students are seven teenagers with special abilities, known as "Flowers." Their status as students is merely a cover for their true roles as members of a UN-run intelligence agency. Their mission is to assassinate other teenagers who possess similar abilities. The Flowers must complete their missions without fail. Their organization has taken their family members hostage to guarantee compliance. For the Flowers, failure means death not only for themselves but also for their loved ones. This is the story of their struggle against a cruel fate, and of how human nature finds hope, however bleak the outlook.