"Busou Shinki" is set in a near-future world where miniature humanoid robots, known as Shinki, are popular as both companions and combatants. These Shinki are equipped with customizable armor and weapons, allowing them to engage in battles for sport or competition. The story centers around Rihito, a young man who owns three Shinki: Arnval Mk.2, Strarf Mk.2, and Altlene. Each Shinki has a distinct personality and fighting style, reflecting their unique programming and design.

Arnval Mk.2 is a balanced fighter with a calm and collected demeanor, often acting as the voice of reason among the group. Strarf Mk.2 is more aggressive and competitive, driven by a desire to prove her strength in battle. Altlene, the newest addition to the group, is gentle and nurturing, often providing emotional support to her fellow Shinki. Together, they form a close-knit team under Rihito's care, navigating both the challenges of combat and the complexities of their relationships.

The narrative explores the daily lives of Rihito and his Shinki as they participate in battles, interact with other Shinki owners, and face various challenges. The series delves into themes of camaraderie, loyalty, and the evolving bond between humans and their robotic companions. While the Shinki are designed for combat, their interactions often highlight their capacity for emotions and personal growth, blurring the line between machine and sentient being.

As the story progresses, the Shinki encounter rival teams, each with their own motivations and strategies. These encounters lead to intense battles that test the limits of their abilities and teamwork. The series also touches on the ethical implications of creating sentient robots for entertainment and competition, though it primarily focuses on the personal journeys of the characters rather than delving deeply into philosophical debates.

"Busou Shinki" balances action-packed sequences with moments of lighthearted humor and emotional depth, creating a narrative that appeals to fans of both mecha and slice-of-life genres. The interplay between the Shinki and their owner, as well as their interactions with other characters, drives the story forward, offering a blend of excitement and heartfelt moments.