The titular character of the series. She is the second princess of the royalty, daughter of the king of all monsters. She appears as a young aristocratic woman wearing Gothic clothing. Her real name is Lillian but she dislikes people calling her by it. Although her siblings are busy fighting for the throne, she shows no interest in it. She resurrected Hiro on a whim after he dies, thinking him interesting enough to be her servant. She is not as arrogant as she is playful, and she does not flinch at the sight of violence. In manga she uses her vassal to resurrect warriors for the royalty (her blood) in anime she uses the flame of life. Her aristocratic nature is shown in her ability to leave hard labor to her servants without remorse. She is also not above destroying anything in her path to kill an enemy, and using any weapon at her disposal, such as a chainsaw, a defibrillator, a hammer, or various swords. Interestingly, she is only as physically strong as a normal human and sometimes requires that her servants put her out of trouble or help her defeat an enemy. She also does not hesitate to save her servants, even going as far as breaking the rules to do so.

In the 'Princess Rampage' chapter of the manga, she shows a certain disgust or fright over a mouse Flandre found at the end of the chapter. She also becomes a temporary half-vampire in order to save Hiro in the manga chapter 'Princess Blood'; her relationship with Hiro remains uncertain both in anime and manga however, and it is not known if she sees Hiro as a love interest or just a soldier of the royalty.

(Source: Wikipedia)