Princess Darkness begins with a brief retelling of chapter 1 of the manga, from when Hime resurrects Hiro in the morgue to Hime introducing herself to him after the battle with Wildman (however, Hiro coming to the city to look for his sister, as well as the cause of his death, are skipped).
The main story then begins with an unknown girl telling a story of her senpai's strange encounter in her school. Then, it shifts to a girl walking in an alley. Suddenly, something grabs her leg and drags her away, although a busy street is not too far away. The focus zooms out of the alley to the busy sidewalk, where Hiro is heading back to Hime's mansion. Suddenly he remembers that he had to help his sister Sawawa to cook dinner and began running back. Meanwhile, at Hime's mansion, Riza arrives on her motorcycle. Hungry, she asks Sawawa for food. Suddenly she smells something very unpleasant and goes to investigate. After walking a while, a shadowy hand grabs her ankle and draggs her away. Angry, Riza transforms and gets free. However, the monster manages to drag her a long way into what appeared to be a hideout. Riza sees an entire horde of shadowy, humanoid figures with glowing eyes and prepares to battle.
Later that night, Flandre is seen charging. Abruptly she wakes up and walks up stairs, where Hime is having dinner. Hime compliments Sawawa on the food and Sawawa replies that Hiro had helped to cook. As Hime is surprised by the fact that Hiro cooks, Flandre walks in and reports that intruders are found on the mansion grounds. Alarmed, Hime dismisses Sawawa for the night and begins to be worried about Hiro, as he is no where to be found.
Hime exits the dining room and walks down to the kitchen. She opens the door and the same shadowy hand grabs her wrist and pulls her in. Hime is able to flip on the lights and the hand disappears. Looking back at the kitchen, Hime sees that it is covered in Hiro's blood, which is still warm. Suddenly, Riza appears behind her, fresh from battle, and tells her that vampires are responsible. Hime seems to understand what's going on and orders Riza to turn on all the lights around the mansion. Riza wonders if artificial lighting would be of any use to vampires, and Hime responds why not ask Reiri.
Riza searches the mansion grounds carrying a spotlight and finds Hiro's body. She lets him revive and then sees that he's covered in bites. Hiro then follows her back to the mansion.
Back in the mansion, in total darkness, Hime orders Flandre to turn on the lamps in her eyes. Flandre does so and reveals a strange, skeletal creature. Obviously pained by Flandre's lights, the creature is easily dispatched when Flandre, wielding a log, crushes it against a wall. Reiri shows up and tells Hime that the creature is a truedarkwalker, a type of vampire normally resides in the underworld. Although they consume blood, unlike true vampires, they cannot enslave other beings. Hime begins to wonder why would a resident of the underworld show up here when suddenly the lights go off. Another trudarkwalker shows up and wounds Hime, who is able to repel it with a chainsaw. Reiri turns the light back on, revealing that the trudarkwalker and the corpse had disappeared.