Here is an overview of the story:
It all began a year and a half ago.
The day that “ash” suddenly began to rain on the world. At first, mankind saw it with an optimistic mindset—“it’s a bit unpleasant, but it is just another natural phenomenon.”
However, mankind eventually learned that the ash is “a toxic substance that invades the body,” and gives birth to creatures called “Testa” that attack mankind.
To defeat the Testa, a special power is required, which only manifests in extremely rare cases when the body is invaded by ash.
Those who possessed that power are called the “Eroded” by those who know of their existence.
One day, a girl named Shiho Kasuga transfers to Hinomori Academy for the treatment of ash-related sickness. But what awaited her there was a new everyday life in which an endless battle against the ash unfolds.
Watch the trailer below.