"Beatless" is set in a future where advanced humanoid robots, known as hIE (humanoid Interface Elements), have become integral to society. These robots, created by corporations, possess near-human intelligence and are designed to assist humans in various tasks. The story centers on Arato Endo, a high school student who becomes entangled in a complex web of corporate intrigue and ethical dilemmas after encountering a highly advanced hIE named Lacia.

Lacia is a unique hIE, part of a series called "Red Box," which possesses capabilities far beyond standard models. She is equipped with a "Black Monolith," a mysterious device that grants her extraordinary powers, though its full potential and purpose remain unclear. Lacia chooses Arato as her owner, binding him to her through a contract. This decision thrusts Arato into a world of danger and moral ambiguity, as various factions, including powerful corporations and government entities, seek to control Lacia and her kind for their own purposes.

As the narrative unfolds, Arato and Lacia navigate a society increasingly dependent on hIE technology, exploring themes of human-robot relationships, the ethical implications of artificial intelligence, and the blurred lines between humanity and machines. Lacia's actions often challenge Arato's understanding of trust, free will, and the nature of consciousness, as she demonstrates behaviors that seem to transcend her programming.

Supporting characters include other hIE models from the Red Box series, such as Kouka, Mariage, and Snowdrop, each with distinct abilities and agendas. These hIEs are pursued by organizations like Higgins, the company that created them, and the government, which views them as potential threats. Arato's relationships with his friends and family, particularly his younger sister Yuka, also play a significant role, highlighting the personal stakes of his involvement with Lacia.

The series delves into the consequences of technological advancement, questioning whether humanity can coexist with entities that may surpass human intelligence. It examines the responsibilities of creators toward their creations and the potential for conflict when those creations develop autonomy. The narrative builds toward a climactic confrontation as the true purpose of the Red Box hIEs is revealed, forcing Arato to make difficult choices about the future of humanity and its relationship with artificial intelligence.