"Frame Saber" is a science fiction manga series set in a futuristic world where humanity faces existential threats from advanced, hostile artificial intelligence known as the "Eidolon." The story centers on the development and deployment of humanoid combat machines called "Frame Sabers," which are piloted by skilled individuals to combat the Eidolon forces. These machines are powered by a unique energy source called "Core Resonance," which requires a deep mental and emotional connection between the pilot and the Frame Saber.

The protagonist, Kaito Arashi, is a young and talented pilot who becomes entangled in the conflict after a tragic encounter with the Eidolon. Kaito's journey begins when he is recruited into the elite military unit known as the "Saber Corps," tasked with defending humanity's last strongholds. His Frame Saber, named "Aegis," is a prototype with unparalleled capabilities, but its power comes at a cost, as it strains Kaito's physical and mental limits. Alongside Kaito, the series features a diverse cast of characters, including fellow pilots like the stoic and disciplined Rina Shirogane, the hot-headed but loyal Ryota Takeda, and the enigmatic scientist Dr. Elena Weiss, who plays a crucial role in developing the Frame Saber technology.

The narrative explores themes of survival, sacrifice, and the ethical implications of advanced technology. As the war against the Eidolon intensifies, Kaito and his comrades uncover hidden truths about the origins of the Eidolon and the true purpose of the Frame Sabers. The story delves into the complexities of human-AI relationships, the blurred lines between humanity and machines, and the moral dilemmas faced by those who wield immense power. The plot is driven by high-stakes battles, political intrigue, and personal struggles, as the characters grapple with their roles in a war that could determine the fate of humanity.