Murumuru appears as a deeply enigmatic figure, her entire face perpetually obscured by a mask that conceals eyes and hair. Her origins and past are utterly unknown, providing no insight into her background. She maintains profound silence, rarely speaking and interacting minimally with the other survivors sheltering within the tower.

She lives in a tent positioned near an indoor garden inside the sealed-off Tokyu Kabukicho Tower, an isolated refuge following the zombie pandemic's devastation. Her most frequent utterance, the muttered phrase "A safe zone, huh," cuts through her habitual quiet, leaving a distinct mark despite her reticence. This seclusion reinforces her detached and mysterious presence among the group.

Murumuru exists within the dynamic surrounding the amnesiac protagonist Mikoto Amano, taken in by the survivors after civilization's collapse. When a boy rescued with Mikoto is brutally murdered, exposing a killer among them, the refuge's fragile peace shatters. Murumuru's place in this tense scenario remains ambiguous, defined solely by her silence and physical concealment, not by overt actions or expressed motives.