After 2.5 years of fighting with an alien species known as the Wilted, humanity’s forces were ultimately defeated when the enemy finished implanting the Wither—a type of planetary virus that would slowly change the conditions of their planet, Flos, into ones that were only suitable for the Wilted. Understanding their technological disadvantage, world militaries began surrendering, and in respect for realizing that senseless fighting led to nowhere, the Wilted agreed to not finish invading Flos until the planet finished its transformation, giving humanity time to come to terms with their demise.

Lily, an Esper cursed with the ability of perfect memory, was the only survivor in her squadron of five. After questioning the meaninglessness of her survival, she takes it upon herself to travel the world and fulfill her role as the team's memory keeper, with the ultimate goal of reaching the place where they had first met—a place they called “the edge of the world.”