From the introduction: Welcome, welcome, to Mermaid. What’s that? You haven’t heard of Mermaid? Oh yes, of course, how silly of me. Well, here’s the short answer to that question. Mermaid is a prison in a modern world much like yours that, or, more specifically, your prison. You see, this whole world is “suffering” from a plague called the ‘Armed Virus,’ so named because it literally allows the direct weaponization of the human body. All people, or rather, exclusively women, who show signs of the virus on any routine medical check, or from “activating” with another carrier are forcibly removed from their families and lives, for their own safety, and are isolated on islands just like Mermaid for quarantine and ‘observation.’