"Fantastic Detective Labyrinth" is a supernatural mystery anime that revolves around Hyuga Mayuki, a young boy who becomes entangled in a series of bizarre and otherworldly events after the mysterious disappearance of his father, a renowned archaeologist. The story begins with Mayuki encountering a strange, sentient puppet named Sakuya, who claims to be a detective investigating supernatural phenomena. Together, they embark on a journey to uncover the truth behind Mayuki's father's disappearance and the enigmatic "Labyrinth," a hidden world filled with supernatural entities and ancient secrets.

As Mayuki and Sakuya delve deeper into their investigation, they encounter a variety of characters, each with their own connection to the Labyrinth. Among them is Mayuki's childhood friend, Nanami, who becomes a key ally in their quest. The narrative unfolds through a series of episodic cases, each involving supernatural occurrences tied to the Labyrinth. These cases often involve solving puzzles, battling malevolent spirits, and uncovering hidden truths about the characters' pasts.

The Labyrinth itself is a central element of the story, depicted as a mysterious, ever-shifting realm that exists parallel to the human world. It is inhabited by beings known as "Shikigami," supernatural entities that serve various roles within the Labyrinth. The Shikigami are bound by contracts and often play pivotal roles in the unfolding mysteries. As Mayuki and Sakuya progress, they learn that the Labyrinth is not just a physical place but also a manifestation of human desires, fears, and memories.

The series explores themes of identity, memory, and the blurred line between reality and illusion. Mayuki's journey is as much about self-discovery as it is about solving the mysteries surrounding his father. The narrative gradually reveals connections between the characters and the Labyrinth, culminating in a deeper understanding of the forces at play and the true nature of the Labyrinth itself.

"Fantastic Detective Labyrinth" combines elements of mystery, fantasy, and psychological drama, creating a layered and engaging storyline. The interplay between the human world and the supernatural realm, along with the evolving relationships between the characters, drives the narrative forward, making it a compelling exploration of both external and internal mysteries.