"Reinō Tantei Miko" centers around Miko Mido, a high school girl who possesses the unique ability to communicate with spirits. This ability, inherited from her grandmother, allows her to see and interact with the supernatural world, which remains invisible to most people. Miko uses her gift to solve mysteries and help spirits find peace, often encountering restless or vengeful entities tied to unresolved issues from their lives. Her investigations frequently involve uncovering hidden truths, resolving emotional conflicts, and confronting malevolent forces that threaten both the living and the dead.

The narrative unfolds as Miko takes on various cases, each presenting a distinct supernatural mystery. These cases range from haunted locations to personal hauntings, often tied to the unresolved emotions or regrets of the spirits involved. Miko’s investigations are aided by her sharp intuition, her ability to communicate with spirits, and her determination to bring closure to both the living and the dead. Alongside her is her friend and classmate, Keiichirou Hoshino, who provides support and grounding, often acting as a bridge between Miko’s supernatural world and the ordinary human perspective.

The series explores themes of loss, redemption, and the lingering impact of unresolved emotions. Each case delves into the backstory of the spirits Miko encounters, revealing their struggles, regrets, and desires. The interplay between the human and spirit worlds is a recurring motif, highlighting the interconnectedness of life and death. Miko’s journey is not only about solving mysteries but also about understanding the complexities of human emotions and the consequences of actions, both in life and beyond. The narrative maintains a balance between episodic cases and an overarching progression, gradually revealing more about Miko’s abilities, her family’s history, and the broader supernatural forces at play.