Kate is the police captain, responsible for upholding the law in Alchem City. After years of hard work and being looked over for a promotion, she turned to the Dark Alchemist for help. The Dark Alchemist promised to promote her to Police Chief once he rules Little Islands. In return, she must help certain key villains escape the law while he mobilizes his forces.
Each mastery level adds another card to the cardpool for defeating Kate. Each of the bronze, silver, and gold mastery levels unlocks a new card, while it takes all three diamond and onyx levels to unlock a single card.