Muu serves as a companion to the protagonist within the Middle World, a realm existing between the World of the Living and the World of the Dead. The character's journey unfolds across multiple episodes, revealing significant development through interactions and pivotal events.

Muu forges a deep emotional bond with others in the Middle World, a connection explicitly explored in a dedicated episode. This relationship becomes a narrative focus, showcasing Muu's capacity for care and loyalty. Later, Muu demonstrates agency and capability, taking decisive action that shapes the journey through the Middle World. This moment highlights the character's growth and evolving importance.

Muu's story arc culminates in a departure marked by an episode centered on farewell. This exit signifies the completion of the character's role within the overarching quest narrative, where various beings assist the protagonist.

Muu's presence contributes to themes of assistance and companionship amidst the challenges encountered in the Middle World.