This slice-of-life battle series takes place in a future that has seen neither World War III nor an alien invasion—simply an ordinary era following our current age. In this society, robots are integrated into daily life and play various roles. "Shinki" are cute partners, standing 15 centimeters (about 6 inches) tall, designed to assist humans. Possessing intelligence and emotions, they dedicate themselves to serving their "Masters." These Shinki can also be outfitted with weapons and armor to engage in combat with one another. Such units are called "Busou Shinki" (literally, "armed divine princesses"). Specifically, the Shinki Ann (Arnval), Aines (Altines), and Lene (Altlene) serve a high school freshman named Masato. The dynamic shifts when a new, bellicose Shinki named Strarf joins their group.