There is often some sort of conservation of lifespan where the victim's life is added to the immortal's and the victim dies so that the immortal can continue to keep living. This form of immortality usually grants eternal youth and the feeding process may actually cause the victim to grow older because the victim's youth is being drained into the immortal.
If such an immortal doesn't feed, they will eventually die.
Comparable and closely related to Blood Bath, where a character attains life or power by immersing oneself in the vital essence of his/her victim(s), rather than by consuming it.
Subtrope of Immortality.
Although this type of immortality could be described as vampiric, only sometimes does it apply to actual vampires. Vampires usually won't die from a lack of blood.
- Shinigami in Death Note. When a Shinigami kills a human, that human's lifespan is added to the Shinigami's. Shinigamis who don't kill regularly will die.
- Kurobara Alice: Vampires can drink each other's blood to extend their lifespan, but it will shorten the blood-source's life by the same amount. Becomes a vehicle for some serious Angst when a sympathetic character is revealed to be short-on-time.
- In Zettai Karen Children, both Fujiko and Kyousuke have bodies of healthy adolescents while they are actually in their 80s. Fujiko accomplishes this by energy-drinking kissing (it's implied that she doesn't do any long-term damage to her "victims"), while Kyousuke (who is, paradoxically, at least initially perceived as the Big Bad of the series) explicitly says that he detests doing something like this, so he accomplishes this in some other ways (probably biochemically).
- Morlun from Spider-Man belongs to a race, the Ancients, that maintain immortality by draining life energy from people, especially people who are an animalistic totem.
- X-Men villainess Selene, The Black Queen. A millenia-year old mutant who can drain the life out of others to keep herself young. As an added bonus, said lifeforce also fuels her sorcerous powers.
- A Wonder Woman comic had a No Celebrities Were Harmed version of Walt Disney named Wade Dazzle who was being kept alive by life force drained from visitors to his theme park and fed into his preserved body.
- The Wraith from Stargate Atlantis, who feed on something from their victims that causes them to age rapidly. It's implied to be life force, but never actually spelled out.
- Javna, a demon from Charmed. He needed to regularly steal the youth of his victims, aging them into old people, in order to retain his youthful form. If he doesn't, he ages rapidly.
- The Twilight Zone:
- One episode featured a man who found that he could obtain abstract or otherwise normally non-transferable attributes from other people by simply making the deal with them. Among other attributes, he restored his youth by "buying" it from younger men who thought him to be a kook giving them money for nothing. He only took a year from each man, but was able to become young again. Incidentally, he was only an old man because he had previously sold his own youth to an elderly millionaire (he came out financially ahead after the exchanges were complete).
- Another episode involves a movie queen who retains her youthful appearance by stealing the life force of others.
- "Queen of the Nile". A woman uses a scarab beetle to drain the life force of men so she can maintain her eternal youth. It's implied that she's the actual Cleopatra of Egypt.
- Ampata, from Buffy the Vampire Slayer's "Inca Mummy Girl". She was an Andean mummy who sucked living humans' life forces dry to stay alive herself.
- Angel did it in the tie-in short story collection "The Longest Night". A man was killing people by using a demon's help to steal their youth, because he was desperate to see his son grow up. He tries it on Wesley, and when Angel gets there, it's the boy who's growing older while Wes becomes an old man, at least until Angel manages to break the spell.
- Magnus Greel in the Doctor Who serial "The Talons of Weng-Chiang" attempted to stay alive by draining the life essence out of young women. Leela only just avoided suffering this fate.
- Kolchak the Night Stalker episode "The Youth Killer". Helen of Troy has survived to the present day by sacrificing perfect human victims to the goddess Hecate. The sacrifice is made by magically causing Rapid Aging in the victims, which in turn gives Helen eternal youth.
- Supernatural in the episode "Something Wicked" an immortal creature called a shtriga drains the life force from people, mostly children.
- Variant in Highlander: The Series. Immortals will remain so without any life-sucking, but if they behead another immortal they absorb their knowledge and skill.
- Lord Voldemort in Harry Potter and The Philosopher's Stone stays alive by drinking unicorn blood.
- Elric will use his sword Stormbringer to drink the souls/lifeforce of the beings he attacks.
- The Kurians of the Vampire Earth drink life force through their vampiric avatars, who live off the blood of the victims.
- The New World of Darkness supplement Immortals details a number of types of people who have managed to overcome the limitations of age—generally through this trope.
- In the fan-made New World of Darkness game Genius: The Transgression, all "manes" (creatures created in realities produced by the excess mental energy of dis-proven theories), orphans (Mad Scientist inventions that have broken loose and gone mad), and any Genius who takes it have the "Calculus Vampire" merit which allows them to drain Mania (essentially mad science/brainpower as a sort of energy), which the first two groups must feed on.
- In Dungeons & Dragons, there is a prestige class that lets you do this in the book Faiths of Eberron.
- Reaver of Fable II, who keeps his youth through the centuries by sacrificing the youth of innocents to the Shadow Court.
- Metroids do this, using their claw/fangs to latch onto a creature and sucking the life out of it, leaving behind a withered husk that crumbles into dust at the slightest touch. This is also implied to be the reason that most weapons to not affect them: they channel absorbed energy into a natural forcefield that defends against attacks. It is not made clear whether or not a Metroid ever dies of old age.
- The monster in France from El Goonish Shive was a former human who achieved immortality by draining the lives of young women.
- Justice League had an episode featuring Morgan Le Fay surviving this way.
- In a Totally Spies! episode, the big bad is using some kind of magic stone to absorb youth from kids, resulting in this trope. As soon as aforementioned magic stone is destroyed, No Immortal Inertia is triggered.
- Star Trek: The Animated Series episode "The Lorelei Signal". The women of the planet Taurus II drain the Life Energy of men to maintain their own youth, which causes Rapid Aging in the men.