In a world divided by wealth and poverty, four young girls are taken into an orphanage run by the shadowy organization Black Knight. Trained as assassins, BlackMind, BlackHeart, BlackBeauty, and BlackHand become elite operatives, their sisterhood forged through shared suffering and skill. When Blackmind is severely injured and discovers a world beyond violence, the sisters must decide between loyalty to their deadly mission or risking everything for a chance at freedom.