Allan Menzies said Akasha, the heroine of a film he watched more than 100 times, had constantly repeated her instructions to kill, most recently last week.
"The more [deaths] the better ... it keeps her happy," he said.
He added that both he and Akasha were disappointed by the State Hospital at Carstairs, where he has been held for several months while awaiting trial. "There’s no other vampires," he explained.
Before he gave evidence, the jury at the High Court in Edinburgh heard from a psychiatrist about the "real possibility" that Menzies had invented fantasies about vampires to avoid a conviction for murder.
Menzies was said to have a personality disorder, but no mental illness, when he repeatedly beat and stabbed Thomas McKendrick to death. "I suspect his enjoyment of violence is the principal factor in the prolonged and excessively violent nature of this crime," said Derek Chiswick, a consultant forensic psychiatrist.
Menzies, 22, of Fauldhouse, West Lothian, is accused of murdering Mr McKendrick, 21, of Church Place, Fauldhouse, on 11 December last year and burying the body, which was not found for five weeks.
The Crown has rejected a guilty plea by Menzies to the lesser offence of culpable homicide, on the ground of diminished responsibility.
Menzies said he never stopped playing a video of the vampire film, Queen of the Damned, after Mr McKendrick had loaned him a copy in August last year.
The character, Akasha, played by Aaliyah, an American singer, was the queen of the damned and she appeared before him and spoke to him. "It ended up I agreed with her... I would murder people and be rewarded in the next life. I would be made immortal, a vampire," said Menzies.
He claimed Mr McKendrick made an insulting, sexual comment about Akasha when the two men were in the kitchen of the accused’s home. Akasha was standing there, but said nothing.
"It was the look on her face. She was not pleased. Then, she turned her back on me. I thought it was because Thomas had insulted her and I let him away with it," Menzies told the jury.
He said he attacked Mr McKendrick with a bowie knife, a kitchen knife and a hammer.
"When she turned her back on me, I felt I had let her down. At the end of the day, I knew I would have to murder somebody anyway, so ... if you did not murder somebody you could not become a vampire."
He described drinking two cups of Mr McKendrick’s blood and eating a fragment of his skull. "I looked in the mirror to make sure my teeth were covered with his blood."
Menzies said he now believed he was a vampire and had achieved immortality. Akasha had continued to visit him since the killing and told him to do it again. "That is what we ... vampires ... do." Asked if he wished he could turn back the clock, he replied: "No."
Menzies had attempted suicide after the killing, but he said that was "to get to the next life quicker ... that’s when I will be rewarded". And although he was sorry for Mr McKendrick’s family, he otherwise felt "nothing, really".
He said he had seen Akasha in his room at the State Hospital. They had both been disappointed, because "there’s no other vampires in Carstairs". He denied making up the fantasies. "People tried to tell me she was not real and I could not see her, but that’s bulls***."
Earlier, Dr Chiswick said there was clear evidence that Menzies was emotionally disturbed and had a psychopathic personality disorder. The accused was particularly interested in the consequences of violence and the infliction of pain on others, but these were part of the disorder and not features of mental illness.
"I do not consider at the time of the offence he was suffering from any form of alienation of reason arising from any mental illness," said Dr Chiswick.
Asked what purpose Menzies would have to exaggerate fantasies about vampires, Dr Chiswick said: "It does occur to me as one possibility that they are manufactured to avoid conviction for a crime of murder.
"The other possibility is they are used by him to psychologically cope with an appalling and horrific act of violence that perhaps he cannot explain himself."
Dr Chiswick said that shortly before Menzies was detained by police, he had spent 48 hours in hospital after taking an overdose. At that time, he had made no mention of the fantasies.
"They have developed over time and it makes me suspicious that the first option, that these have been manufactured, is a real one that has to be taken seriously," said Dr Chiswick.
The trial continues.