Fumika works as a mail carrier transporting letters penned by the deceased, each holding unspoken messages—unresolved emotions, concealed secrets, or clues to crimes like murder. She navigates a liminal realm detached from the living, aided by a sentient, levitating staff that assists in logistical tasks. While other carriers exist as ageless spirits, Fumika ages, marking her as neither dead nor fully alive but suspended in astral projection.

Her stoic, monotone presence clashes with her staff’s loud, animated demeanor. Interactions with cats provoke visible distress, disrupting her composure, while insects trigger aversion in the light novels. She pursues her delivery duties relentlessly, even confronting resistant recipients with coercion or force when necessary.

A fractured psyche defines her past: childhood abuse by her father, Kirameki Mikawa, fractured her identity into two personas. Mika embodies dutiful resolve, fixated on her role, while Fumi retreats into fragility. This dissociation originated as a survival tactic during prolonged trauma. The split crystallized when Mika fatally shot Kirameki to protect Fumika after he turned violent, haunted by memories of her mother. Post-trauma, Fumi withdrew into a comatose state, rendering Mika dormant. The personas remain divided, their communication strained and incomplete.

Novels depict her intuitive shogi prowess and her staff, Mayama—a male-voiced, sarcastic companion—while the anime replaces him with Kanaka, a spirited female-voiced counterpart. Literary adaptations also accentuate her entomophobia, omitted in animated portrayals.

Encounters with former classmates, including a high school student clinging to unspoken affections, underscore her tenuous ties to the living. These meetings sporadically surface memories of her past, though her mission dominates her focus. Episodic exchanges with recipients unravel her psychological layers, threading together her trauma and the dual identities warring within her.