Quele Sellier serves as a Grim Reaper and is a distant cousin of Lisara Restall. She addresses Lisara as "Onee-sama," despite their lack of a direct sibling bond. Quele forms a power contract with Mina Okura, drawing sustenance from Mina's emotional energy—especially feelings tied to Ryosuke Kaga—a situation causing dismay for both Ryosuke and Lisara.

In human guise, she possesses ochre hair and brown eyes. Her Grim Reaper transformation manifests an appearance reflecting her elemental affinity for ice and water, contrasting sharply with Lisara's fire-based nature. She wields the gladius "Carnun Solace," a conduit for her ice magic. Her techniques encompass "Disrado" for transformation, "Skill Nil" to create concealed battle domains, and "Astalphe" to generate defensive shields or orbs. Quele also commands memory-altering abilities, capable of erasing recollections of specific events.

Characterized as treacherous, cunning, opportunistic, and manipulative, Quele presents a facade of cheerful innocence while actively undermining Lisara. Her personality blends sadistic tendencies and a smarmy demeanor with a reserved, level-headed core. She harbors romantic feelings for Ryosuke Kaga, influencing her initial actions.

Quele's narrative involves a profound shift in loyalty and motivation. Joining the central conflict triggers her evolution from antagonist to ally. She sets aside her own affection for Ryosuke, choosing instead to support Mina's feelings and later, Lisara's relationship with him. This transformation culminates in her actively aiding the protagonists against threats, marking a redemption arc where initial deceit yields to genuine cooperation. Her development underscores a transition from self-serving manipulation to protective solidarity within the group dynamic.