"Yurei Deco" is set in a futuristic, digitally-driven society where virtual and physical realities are deeply intertwined. The narrative unfolds in Tom Sawyer, a city where every aspect of life is governed by a system called "Deco," which quantifies social interactions, emotions, and even personal worth through a numerical score. The story centers on Berry, a young girl who becomes disillusioned with the superficiality of this system. Her life takes a dramatic turn when she encounters Hack, a mysterious hacker who introduces her to the underground world of "Yurei," a group of individuals who exist outside the Deco system and challenge its control over society.

As Berry delves deeper into the Yurei community, she uncovers the darker aspects of the Deco system, including its manipulation of citizens' lives and the suppression of individuality. Hack, who operates under the alias "Phantom Zero," becomes a key figure in her journey, guiding her through the complexities of this hidden world. Together, they confront the oppressive forces behind Deco, including the enigmatic "Zero," a powerful entity that embodies the system's control.

The series explores themes of identity, freedom, and the consequences of a society driven by data and surveillance. Berry's transformation from a passive participant in the Deco system to an active rebel against it forms the core of the narrative. The dynamic between Berry and Hack, as well as their interactions with other members of the Yurei, drives the plot forward, revealing layers of intrigue and moral ambiguity. The story balances action, mystery, and philosophical inquiry, presenting a thought-provoking examination of a world where technology dictates human existence.