Boukyaku no Rakuen I Arsenon Kakusei

is the first volume of the Boukyaku no Rakuen light novel series, written by Taki Tsuchiya and Illustrated by Kinokohime. It was released under the Dengeki Bunko Imprint in March 2021.

Synopsis
A world where the ocean covers most of the earth's surface after repeated conflicts. Lean is a paradise of oblivion where weapons, science, faith, and the fire of all conflicts are managed and concealed in order to control humanity toward destruction. However, the highly toxic pollutant  created by the conflict still eroded people. One day, the boy Arum was ordered to manage the mysterious girl Fluorite who has  in his body. Two people who are clumsy but keep in touch with each other. The secret of  that becomes clear. It was a literal "poison" that shook false peace. What do boys get over the multiple plots over the new world of oblivion? The 27th Dengeki Novel Grand Prize << Silver Award >> winning work.

(source: Dengeki Bunko Official Website - Translated)