"Angel Blade" is a science fiction anime series set in a dystopian future where humanity faces existential threats from both external and internal forces. The narrative centers on a young woman named Nanael, who is part of a genetically engineered group known as the Angels. These Angels are designed to combat the monstrous entities called Devils, which have emerged as a result of humanity's misuse of advanced technology and genetic experimentation. Nanael, despite her initial reluctance and lack of combat experience, is thrust into the role of a warrior due to her unique genetic makeup, which grants her extraordinary abilities.

The story unfolds as Nanael joins forces with other Angels, including the experienced and battle-hardened Aoi, to protect the remnants of human civilization. Their mission is to locate and destroy the source of the Devils, a mysterious and powerful entity known as the Dark Lord. Along the way, Nanael grapples with her identity, the ethical implications of her creation, and the moral complexities of her mission. The series explores themes of survival, the consequences of scientific hubris, and the blurred lines between humanity and monstrosity.

The plot is driven by a series of intense battles between the Angels and the Devils, each encounter revealing more about the origins of the conflict and the true nature of the Dark Lord. As Nanael and her comrades delve deeper into the mystery, they uncover dark secrets about the organization that created them, raising questions about loyalty, free will, and the cost of survival in a world teetering on the brink of annihilation. The series balances action-packed sequences with moments of introspection, providing a layered narrative that examines the psychological and emotional toll of war on its characters.