Basic Trope: The longevity and health of a person is dependent on their Life Energy, which can be stolen.
Straight: Aurora the Witch keeps herself young by stealing and consuming the Life Energy of young women.
Exaggerated: Life Energy is a magical cure all that Aurora markets over late-night TV infomercials, promising it can restore Hit Points, cure Standard Status Effects, rejuvenate the vain, grant longevity, and cure gout.
Inverted: People don't lose Life Energy as they age, they instead accumulate "Death Energy", which causes illness, aging, and eventually death. Extracting "Death Energy" can prolong life and cure illness.
Aurora sucks the life energy out of her victim, and the victim dies. However, Aurora doesn't seem to be getting any better.
Aurora's spells to restore her beauty and extend her life don't suck out young maiden's Life Energy, but instead cause a Freaky Friday body switch.
Double Subverted: ...but then the effect kicks in a month later, and Aurora is young again.
Parodied: Aurora puts the young women in an oversized juice machine to comically "squeeze" the Life Force out of them.
Zig Zagged: People have a spiritual juice that makes them go, except it turns out to have been phelgm, only it's magic phelgm, but Clap Your Hands If You Believe turned it back into phelgm.
All this "Life Energy" bunk is just snake oil masquerading as cosmically significant metaphysics. All of its effects are either placebos, hypnotic, or misattributed with completely rational explanations.
There is no magic of any kind in the setting at all, and diseases work the same way as they do in Real Life. Aurora is just another health scammer.
Enforced: The story has vain and evil witches who want to live forever, so Life Energy is included.
Lampshaded: "Why a kind and loving god would create humans with such an easily stolen thing as Life Energy is beyond me, but who am I to complain?"
Invoked: "Stealing Life Energy should be impossible, but whatever is doing this seems to kill people by sucking something like Life Energy from the mouth. Wear these helmets to protect yourselves."
Defied: Aurora explains she doesn't steal Life Energy or anything of the kind, her magic rejuvenates and enriches by other means. Like creating illusions, or replacing her blood with mercury to always shine and flow brightly.note Anyone who mentions it's highly poisonous and scientifically impossible gets turned into a frog)
Discussed: "The easiest way to steal Life Energy is via kiss. So no matter how pretty she may seem, do not kiss anyone until we find Aurora."
Conversed: "You'd think all these people crazy over virgin Life Energy realized they could get more octane per gallon if they drained someone who's been around the block a few times."
Deconstructed: Aurora comes to view human life as a commodity that can be bought, sold, bottled and drunk. As the poor sell their youth to the rich, society is destroyed as the poor are cannibalized and the rich become immortal.
Reconstructed: Life Energy becomes a metaphor for slavery. The quantifiable value of life prompts people and witches to treat it like Real Life organ theft/selling, as they desperately try to "turn back the clock" and fight "Life Energy Slavery" and theft with any means available.
Played For Laughs: Since everyone has a finite amount of Life Energy that goes down with age and lifestyle, witches and wizards dump the magic spiel and become "Efficiency Experts", carefully measuring just how "Life Fuel Efficient" a given diet, exercise or even lifestyle change is for a client.
Played For Drama: Everyone knows how long they have to live from birth, and barring accident or suicide, it is set in stone.