It was to have been a routine hunting trip. Thor had heard tales of a strange creature in Vanaheimr that stalked both animal and Vanir alike. It hadn’t been seen but the corpses found had been bloodless with only a wound to the neck to indicate how that had happened. Thor declared that he would slay the beast and had dragged along both his friends and his younger brother to do so. They had stalked and hunted the creature for several days.
Then one night it attacked their camp. It was nearly impossible to see in the dark and they were unprepared. Fandral was thrown through a tree first. Then Sif and Hogun were thrown into Volstagg in a tangle of limbs. Loki had fought back to back with his brother before shoving the oaf out of the way. He cried out as he felt the creature’s jaws at his throat. He let lose a blast of seidr to get free and Thor struck the final blow.
That was the last thing Loki remembered until he woke in a strange place with his mother at his bedside. It was she who told him that he had been infected by the creature and had been changed by it. She told him of the old legends of the vampires and that a cure was being searched for.
That was nearly a century ago. To protect both him and others he had been placed in a remote castle in Midgard with mechanical servants to see to his needs and keep him from going on a rampage. He was also sent shipments of a special blood wine his mother had made for him that sated his thirst and helped him grow stronger.