The story in short
Katarina is the daughter of General Du Couteau, who made her an assassin from childhood. The training was brutal, and part of it was testing poisons on herself in small doses.
Her first mission was to kill Demetrius, a low-ranking officer in the enemy army. But she wanted a quick win and some glory, so she slit the enemy commander's throat in his sleep instead. Demetrius struck back with an attack that killed dozens of Noxian soldiers, and her father barely survived. He was furious: the best assassins don't chase glory, and she had shamed the family. So he sent another of his students after her. The attacker nearly took her eye and left the scar above her left eye. Katarina survived, threw Demetrius's head at her father's feet and admitted he'd been right to order her death. Since then she's been trying to make up for it by serving the empire.
