In a near future, an illness called "Cagaster" made ​​its appearance. It turns humans into insects. The story begins 30 years after the onset of the illness, in 2125. It follows the adventures of Kidou, a boy who fights insects.

Light showers accompany falling cherry blossoms as they flood the view of another April morning, marking the start of a new school year for students Homi Moegi, Ren Aikawa, and Yua Nakabeni. Discovering that they all share the same class, the three playfully reunite as the new semester begins. Starting another important time of their lives, the girls deepen their friendship through laughter, happiness, sadness, and all other struggles that come their way—all the while wearing dazzling, silky nylon tights. [Written by MAL Rewrite]

By chance, Ryo has slipped from the 1980s into the future, and is trying to get back. In the interim, he's working for the police force of the future, solving cases by applying his unique and often comical approach. (Source: ANN)

In a dark void known as the Lightless Realm, a group of children meet and bond, but are then separated and returned to their own dimension. Years later, these children reunite to fight "Admonitions," monsters that originate from the same void, using robots known as "Vess." However, their efforts only slow the ever-encroaching and expanding Lightless Realm from infecting their world. Their lives take a drastic turn when a new foe appears in the form of a "Corpse," whose song is rumored to kill any who hear it within nine days. The "Corpse Song" is heard by the group, and with this, they each begin to pull away and become caught up in their own personal problems—ultimately threatening the fate of humanity.