"You are changed. Your blood-thirst is replaced by a deeper need - you have become a devourer of souls. To sustain your strength, you must hunt the lost spirits of the Underworld, and consume the souls of your enemies."
User can absorb souls, while removing them from the source, into their body and use it in various ways, gaining some form of advantage, either by enhancing themselves, gaining the drained power, using it as a power source, etc., either temporarily or permanently.
Common advantages include adding the target's skills and abilities to users or using the absorbed souls to augment the user's own powers.
May only be able to absorb certain kinds of souls, such as those belonging to supernatural beings.
Absorbing the captured into the user's self may pose some inconsistencies, as that would then mean that at least two souls must now inhabit the same physical body.
While the user could also absorb elemental-based spirits without any difficulty, most elements can be extremely dangerous for the user to absorb, resulting in nasty outcomes. For example, if the user happens to absorb a soul that is of poisonous origin, the user could suffer and then physically die.
Kathy Newman (Buffy the Vampire Slayer) stealing a soul.
A Soul Eater (Angel)
Charon (Charmed), a Soul Collector, can steal the souls of others, preferably good witches, and transport said souls to Hell.
Dementors (Harry Potter) can drain the souls of humans via the "Dementor's Kiss."
Freddy Krueger (A Nightmare on Elm Street) absorbs the soul of his victims to become more powerful...
... the absorbed souls appearing as screaming faces embedded in his chest.
After absorbing the 30-40 million souls of Purgatory, Castiel (Supernatural) was endowed with god-like power.
Daemon Ritus (Scooby-Doo; 2002 film)
Alexia (Los Protegidos) it can absorb the soul of the people
When the souls of the Migar Prisoners (Tracker) were brought to Earth, they took over human 'hosts' - absorbing the human souls into their own to ensure their survival - but killed the human inside in the process.
Cole (Tracker) is able to use his Collector to capture and entrap the souls of the Migar prisoners.
Kai (Kung Fu Panda) uses Dark Chi Manipulation to steal the souls of his victims.