"Solty Rei" is set in a futuristic city where society is divided between the affluent upper levels and the impoverished lower levels. The story centers on Roy Revant, a gruff and emotionally scarred bounty hunter who lost his daughter in a catastrophic event known as the "Blast Fall," which devastated the city years prior. Roy’s life takes an unexpected turn when he encounters Solty, a mysterious young girl with advanced cybernetic enhancements and no memory of her past. After saving Roy from a dangerous situation, Solty becomes a part of his life, and the two form an unlikely bond as they navigate the complexities of their world.

As Roy and Solty work together on bounty-hunting missions, they uncover secrets about Solty’s origins and her connection to the powerful RUC Corporation, which dominates the city’s technological advancements. The RUC Corporation is revealed to be involved in unethical experiments, including the creation of "Resembles," cybernetically enhanced humans with extraordinary abilities. Solty is revealed to be a unique Resemble, designed with a core that grants her immense power, but her existence poses a threat to the corporation’s agenda.

Throughout the series, Roy and Solty encounter a diverse cast of characters, including Ace, a skilled and enigmatic mercenary; Miranda, a compassionate doctor who aids Roy and Solty; and Rose Anderson, a high-ranking RUC executive with her own hidden motives. The narrative explores themes of loss, redemption, and the ethical implications of technological advancement, as Roy grapples with his past trauma and Solty seeks to understand her identity and purpose.

The plot intensifies as the RUC Corporation’s experiments spiral out of control, leading to conflicts that threaten the stability of the city. Roy and Solty must confront their own vulnerabilities and the moral dilemmas posed by the world they inhabit. The series builds toward a climactic resolution that ties together the personal struggles of the characters with the broader societal issues at play, culminating in a poignant exploration of humanity and connection in a technologically driven world.