This one's based on "Daughter of Evil". Riliane is a spoiled princess (well, she's actually a sovereign since her mother died, just waiting to come of age for an official coronation as a queen) who loves having people executed on whim (and I always head that vague idea in my head for a guro story where it is revealed she loves executions so much because she secretly wants to be executed herself), and Allen is her loyal servant who "just so happens" to look just like her (known to him but unknown to her he's actually her twin brother).