"Beatless" is set in a near-future world where advanced humanoid robots, known as hIE (humanoid Interface Elements), have become integral to society. These robots, created by corporations, possess artificial intelligence and are designed to assist humans in various capacities. The story centers on 17-year-old Arato Endo, a high school student living in a world where hIEs are commonplace. His life takes a dramatic turn when he encounters Lacia, a highly advanced hIE with a mysterious black coffin-like device. Lacia is one of five ultra-sophisticated hIEs known as "Red Box" models, each possessing unique capabilities and a level of autonomy far beyond standard hIEs.

Lacia forms a contract with Arato, making him her owner. However, her true purpose and the nature of her advanced intelligence remain shrouded in secrecy. As Arato becomes entangled in Lacia's world, he discovers that she and the other Red Box models are at the center of a complex conflict involving powerful corporations, governments, and societal tensions over the role of AI in human life. The Red Box models are not merely tools but entities with their own agendas, raising questions about the ethical implications of AI and the boundaries between humans and machines.

Throughout the series, Arato grapples with the moral dilemmas posed by Lacia's actions and the broader implications of AI integration into society. Lacia's decisions often challenge Arato's understanding of trust, autonomy, and humanity, as she operates with a logic that transcends human comprehension. The narrative explores themes of coexistence, dependency, and the evolving relationship between humans and AI, set against a backdrop of corporate intrigue and technological advancement.

The supporting cast includes other Red Box models, such as Kouka, Mariage, and Snowdrop, each with distinct personalities and roles in the unfolding conflict. Arato's relationships with his friends and family, particularly his younger sister Yuka, provide additional layers to the story, highlighting the personal and societal impacts of living in a world dominated by advanced technology. The interplay between human emotions and the cold logic of AI drives much of the tension and drama in the series.

"Beatless" presents a thought-provoking exploration of a future where the line between human and machine blurs, examining the consequences of technological progress and the ethical challenges it brings. The story balances action, philosophical inquiry, and character-driven drama, offering a nuanced portrayal of a world on the brink of a new era defined by artificial intelligence.