Mushikago no Cagaster

A global catastrophe thirty years ago, responsible for the deaths of two-thirds of humanity, was not caused by disease but by strange insects capable of transforming people into hybrid creatures that evolve into massive, destructive monsters. These creatures, known as Cagasters, are hunted by exterminators like Kidou, who target them during their brief, partially human stage. To survive the dangers of their work, exterminators often isolate themselves from others. Kidou is assigned to return a young survivor to her mother, a task that forces him to confront the possibility that his emotional detachment may not be as complete as he once thought.