Loki is the protagonist of Mythical Detective Loki Ragnarok. He is the Norse god of mischief who has been exiled to the human world by the chief god Odin for taking his pranks too far. As part of his punishment, he is forced to take on the form of a human child, roughly eight years old, with short brown hair and green eyes. In his true adult form, he appears as a tall young man with lighter brown hair. Loki runs a detective agency called Enjaku Detective Agency, which specializes in paranormal cases. His primary motivation is to collect evil auras that take over human hearts, as this is the only way he can earn the right to return to the realm of the gods and regain his original body and power.

Loki possesses the personality of a classic trickster. He is clever, witty, and often mischievous, with a sharp tongue and a tendency to manipulate situations to his advantage. However, beneath this playful exterior, he is also stoic, somewhat melancholic, and burdened by the weight of his exile and the constant threats from other gods. While he initially appears aloof and self-serving, he gradually shows a caring side, particularly toward those who earn his trust. He is patient and analytical in his detective work, demonstrating a keen intellect and a deep understanding of human and supernatural behavior.

In the story, Loki serves as both a detective and a target. While he solves paranormal mysteries to collect evil auras, he is also hunted by other Norse gods who have been sent by Odin to assassinate him. This dual role places him in a constant state of tension between his mission and his survival.

Key relationships include his loyal companion Yamino, who is actually his son Jormungandr, the great serpent of Norse mythology, in human form. Yamino acts as his caretaker and ally. Mayura Daidouji is a human girl obsessed with mysteries who becomes Loki's self-appointed assistant. She adds a lighthearted and energetic element to his otherwise serious life, and he comes to care for her deeply. Other important figures include Thor, who appears as a poor freeloader despite being tasked with killing Loki; Heimdall, a dangerous assassin; Freyr and Freya, who have their own agendas; and Loki's other children, Fenrir and Hel, who play significant roles in the later parts of the story.

Throughout the series, Loki undergoes notable development. He begins as a detached figure focused solely on his goal of returning to Asgard, but his time in the human world and his bonds with Mayura and others cause him to reassess his priorities. He shows increasing willingness to protect those close to him, even at the cost of his own ambitions. In the final episodes, he makes a difficult choice to erase Mayura's memories of the gods and return to the divine realm, showing both his sense of duty and his deep affection for her.

Loki's abilities include shapeshifting, allowing him to alter his appearance at will, and mastery of illusion and deception. As a god, he has enhanced physical capabilities and knowledge of the supernatural. He is highly skilled in deduction and strategy, using his cunning to solve mysteries and outwit his enemies. In moments of great need or emotional intensity, he can temporarily revert to his adult form, which gives him access to greater power. His most notable ability is his talent for manipulation and trickery, which he uses both as a detective and as a survivor in the world of gods.