Mayu Murasaki is a descendant of the Yuragi Shin, carried within the Mahou Senshi Rin, whom she affectionately calls "Mama." Her physical appearance is exceptionally unusual among Yuragi. Unlike others with red-glowing eyes and human-like features, Mayu possesses large, bright yellow eyes, white shoulder-length hair, and a distinctive collar of roughly twelve octopus-like tentacles encircling her neck. She often wears a dress and a hairbow. Though possessing the stature of a fifteen-year-old teenager, her behavior is energetic, childlike, naive, and intensely curious. She expresses deep affection for Rin, frequently praising her beauty, yet this sweetness masks a brutal monstrous nature inherited from Shin. Any perceived lack of reciprocal love from Rin triggers Mayu's rage, resulting in traumatic consequences for her.

Mayu refers to Shin as "Onii-chan" (brother), creating a contrast with her acknowledgment of Rin's maternal role. Her unusual traits, including the tentacle collar and inability to produce the ringed purple tentacles typical of Yuragi, imply she may be a hybrid entity rather than pure Yuragi. Shin describes her current state as a "caterpillar" phase. To fulfill her purpose as a key to a new world, she must undergo pupation and metamorphosis fueled by high-potency bodily fluids extracted from the Mahou Senshi Ai, Rin, and Meg.

Within the Yuragi hierarchy, Mayu and Shin orchestrate coordinated attacks using the Yuragi army, diverging from their typically solitary behavior. Their collective goal involves possessing and corrupting humans to advance a doomsday plan aimed at destroying civilization. Mayu actively participates in capturing the magical warriors Ai, Rin, and Meg, subjecting them to torture to harvest the necessary fluids for her metamorphosis. Her actions are driven by loyalty to Shin's objectives, positioning her as a central antagonist against the magical warriors.