December, codenamed Dece, operates among the Twelve Sisters—android assassins serving Madame Marciano’s Criminal Guild. Created alongside October and November as one of three identical triplets, her childlike frame mirrors a five-year-old’s, yet houses superhuman strength she favors over her assigned MP5K submachine gun.

Her personality blends immaturity with a penchant for treating lethal missions as games, retaining a playful demeanor even amidst carnage. She frequently dozes during operations, flouting professionalism, yet executes ruthless violence without hesitation—crushing buildings to eradicate targets or reveling in chaotic destruction.

Born from Madame Marciano’s infertility, December was engineered by scientist Neilson as a synthetic heir, addressing her “Mother’s” void. She demonstrates fierce, if impulsive, loyalty to Marciano, obeying April’s leadership alongside her siblings. Though emotionally nuanced, mimicking human joy in chaos, she lacks moral comprehension, aligning purely with the Guild’s mandates.

In combat, her resilience mirrors engineered durability: artificial musculature enables agility and raw power, while her armored frame resists small-arms fire. However, heavy artillery can cripple her, as demonstrated when Sister May persists functionally after decapitation. December thrives in synchronized missions with her triplets, though distractions—trivial or mischievous—often divert her focus.

Her arc resists evolution, cementing her as Marciano’s unwavering enforcer. While the Sisters’ allegiance occasionally bends to individual whims, December’s role concludes ambiguously, her fate unresolved as Guild conflicts leave some siblings surviving, others fallen.