"Full Metal Panic!" is a manga series that blends military science fiction, mecha action, and comedic elements. The story is set in a world where advanced military technology, particularly Arm Slaves (AS), humanoid combat robots, plays a central role in global conflicts. The narrative primarily revolves around Sousuke Sagara, a young soldier raised in war-torn regions and trained by the covert anti-terrorist organization Mithril. Sousuke is assigned to protect Kaname Chidori, a high school student who is unknowingly linked to a mysterious phenomenon known as the "Whispered," individuals with innate knowledge of advanced technology and black science.

Sousuke's mission is to guard Kaname from various threats, including terrorist organizations and rival factions seeking to exploit her latent abilities. His military background and lack of social skills often lead to comedic and awkward situations as he attempts to blend into her everyday school life. Despite his stoic demeanor, Sousuke gradually forms a bond with Kaname, who initially finds his overprotective and militaristic behavior frustrating but eventually grows to trust and care for him.

The plot expands as Mithril uncovers a larger conspiracy involving the Whispered and their connection to cutting-edge technology. The series introduces antagonists such as Gauron, a cunning and ruthless mercenary, and Amalgam, a shadowy organization with its own agenda. These adversaries challenge Sousuke and Mithril, leading to intense battles and strategic confrontations. The narrative also explores the ethical implications of advanced weaponry and the personal struggles of its characters, particularly Sousuke's internal conflict between his duty as a soldier and his desire for a normal life.

Key supporting characters include Melissa Mao and Kurz Weber, fellow Mithril operatives who provide tactical support and camaraderie. The series balances its action-packed sequences with moments of humor and character development, particularly through Sousuke and Kaname's evolving relationship. As the story progresses, the stakes escalate, with global conflicts and personal sacrifices shaping the characters' journeys. The manga concludes with a resolution to the central conflicts while leaving room for further exploration of its richly constructed world.