The Sleeping Prince in the Garbage Dump Episode 1

Angel Trainee Flonne is sent to the Netherworld to assassinate the Overlord, King Krichevskoy. Flonne spends two years searching for Krichevskoy, and eventually wakes his son, Prince Laharl, who doesn't beleive in love. After learning his father has died, Laharl sets out to claim his rightful title of Overlord as heir to the throne, and Flonne decides that she will stay in the netherworld even though her target is already dead to learn the true nature of demons... and possibly carry out the mission with a new target.