Ryouta Murakami has spent ten years carrying the guilt of a childhood friend he calls Kuroneko, who died trying to prove to him that aliens exist; he joins his school's astronomy club to keep that promise. When a transfer student named Kuroha Neko arrives bearing an uncanny resemblance to Kuroneko, she reveals she is a 'witch' with supernatural powers, escaped from a secret research facility. The witches depend on special medication to stay alive, and Ryouta is pulled into hiding and protecting them. Lynn Okamoto's seinen manga sets up this science-fiction thriller.