Daidouji Mayura is a sixteen-year-old high school student and the primary human character in her story. She has long dusty pink hair and large red eyes, and is described as a Japanese beauty. Her most defining trait is a powerful obsession with mysteries, the occult, and all things paranormal. She expresses this enthusiasm frequently with an exclamation of "Fushigi mystery!". Energetic, sweet, and somewhat eccentric, Mayura is also rather impulsive and has a tendency to rush into situations without thinking them through, which often leads her into trouble.

Mayura's background and motivations are rooted in her childhood. After losing her mother at a young age despite praying fervently for her recovery, Mayura lost her faith in gods. This loss of faith is a key part of her character. Her desire to become a detective was sparked by her father, a Shinto priest. When she was a young girl and got lost in an amusement park, her father found her and joked that he could do so because he was a great detective, leaving a lasting impression on her. She is the daughter of a Shinto priest but ironically possesses no sixth sense whatsoever, making her completely unable to perceive the supernatural beings and events that occur around her. This obliviousness is a recurring source of humor and prevents her from discovering that her employer is the Norse god Loki.

In the story, Mayura's role begins when she stumbles upon a possessed doll in a clock tower and seeks help at the Enjaku Detective Agency. Upon meeting the child-like detective Loki, she decides to appoint herself as the agency's helper, believing it will expose her to more mysterious cases. Her key relationships revolve around the agency's members. She develops a close bond with Loki, which by the end of the anime appears to include romantic feelings, though she primarily sees him as a very important person. She also works alongside Yamino, Loki's loyal servant and cook, whose meals she greatly enjoys. Throughout the series, Mayura remains unaware that the strange occurrences she helps investigate are tied to a conflict among Norse gods.

Mayura shows a degree of character development, particularly in the anime's climax. When Loki disappears to return to the world of the gods, Mayura is determined to find him, showing how much she has come to care for him. In a poignant moment, when given a wish by a god (Loki in his true form), her desire is simply to see Loki one last time. This suggests a rekindling of her lost faith. There are notable differences between her portrayals in the manga and anime; the manga version is generally calmer and more perceptive, whereas the anime version is more excitable and prone to shouting about mysteries. Her notable abilities are not supernatural but rather her boundless enthusiasm for mysteries and her persistence in solving them, even when she is completely unaware of their true divine nature.