"Frame Arms Girl" centers around Ao Gennai, a high school girl who receives a package containing a small, sentient robot named Gourai, a Frame Arms Girl. These Frame Arms Girls are highly advanced, humanoid model kits capable of autonomous action and equipped with various weapons and armor. Ao quickly learns that Gourai is designed to gather combat data to improve her AI, and she is tasked with helping Gourai adapt to real-world scenarios.

As Ao and Gourai begin their daily life together, more Frame Arms Girls arrive, each with distinct personalities and abilities. Stylet, a cheerful and energetic fighter, and Baselard, a reserved and analytical type, join the group, followed by others like Materia, Architect, and Hresvelgr. Each Frame Arms Girl has unique traits and combat styles, leading to dynamic interactions and occasional conflicts as they adjust to living with Ao and each other.

The narrative explores the challenges of integrating these advanced machines into human life, focusing on their growth and development as they learn about emotions, teamwork, and individuality. The Frame Arms Girls engage in simulated battles to test their capabilities, often leading to humorous or tense situations. Ao acts as their caretaker and guide, helping them navigate their newfound experiences while balancing her own responsibilities as a student.

Throughout the series, the Frame Arms Girls face various adversaries, including rogue AI units and rival models, which test their combat skills and teamwork. The story also delves into the ethical implications of creating sentient machines, as the Frame Arms Girls grapple with their purpose and identity. The blend of lighthearted moments, character-driven drama, and action sequences creates a balanced narrative that highlights the bonds formed between Ao and her mechanical companions.