Sheffield, presented as Cromwell’s temporary secretary, secretly emerges as the shadow leader of the Reconquista rebellion. Her true loyalty resides with Joseph de Gallia, Gallia’s monarch, whom she acknowledges as her master. Under the pseudonym Mjöðvitnir—translating to "God’s Mind"—she commands a rune bearing the same name, though its precise powers remain undefined.

Strategically, she extends her reach beyond Albion’s political chaos, directing Reconquista’s operations on Joseph’s orders. This includes orchestrating covert maneuvers to weaken Albion’s stability and advance Gallia’s ambitions. Her role as a manipulator is unveiled when Gallian airships annihilate Reconquista’s forces, exposing her true allegiance to Joseph rather than the rebellion.

Her collaboration with Joseph links her to wider schemes, such as exploiting Tabitha’s royal lineage and inciting unrest in adjacent realms. In her final narrative arc, she prioritizes Joseph’s faltering health, insisting on solitude to stay by his side as he approaches death—a gesture underscoring her absolute devotion.

Her status is noted as deceased, with no elaboration on the events leading to her demise.