Blood was important in the Legacy of Kain series; unsurprising as many of the characters - including Kain - were vampires. Blood was necessary for their survival; their blood-thirst was a consequence of the Blood Curse.
In Blood Omen, Blood Omen 2 and Defiance, Kain's body constantly drained his blood reserves, just to stay 'alive'. He needed to feed on blood regularly to sustain his unlife and, more importantly, to heal the wounds he received in battle.
Unlike most fictional vampires, Kain and Vorador could consume blood from a distance, telekinetically drawing it into their mouths from an enemy's body. Vorador was seen doing this in Blood Omen's opening FMV (Full Motion Video). Kain did it throughout Blood Omen and Blood Omen 2. This unusual method of feeding was presumably introduced because of technical limitations and also for gameplay purposes: the 'traditional' vampire bite wasn't practical when fighting many assailants at the same time. In Defiance, Kain could bite or use the telekinetic method, both options being available in-game for the first time.
While the Blood Curse made Nosgoth's vampires "predators of humankind", they could survive, and apparently thrive on non-human blood. Kain drank the blood of a large variety of creatures in Blood Omen and Blood Omen 2, although in the first game, he had to be careful about which blood he drank. Although it wasn't a factor in the later games, blood originally came in four types, identifiable by its colour.[1,2]
In Blood Omen, Kain could also feed from Blood Fountains.
|'Normal' blood that Kain could obtain from humans and some creatures. This would replenish his health.
|Poisonous blood. If Kain drank this, he would become poisoned and his body would need to consume blood far more rapidly to repair the damage it caused. He could be cured instantly with Anti-Toxin Battle Artefacts, but the poison effect would also wear off in time, if he had enough blood to wait it out.
|The blood of ghosts or spirits. If Kain drank this his magical energy reserves would increase, enabling him to cast his spells.
|This would nullify the healing effect of the blood Kain already carried in his body (meaning it reduced the amount of blood that was in his blood vial). He had to avoid drinking it by accident. The Blood Fountains would flow with black blood after Kain had fed from them once.
- [BO2] Janos to the Sarafan Lord: "By what right did you lay on us the curse that drove us from the light, and made us predators of humankind?"
- The Blood Omen Game Manual