"There can be no triumph without loss. No victory without suffering. No freedom without sacrifice."
― Tagline (Lord of the Rings)
The power to gain power from sacrifice. Variation of Affinity.
Users become stronger, faster, more durable, etc. from the sacrifices of oneself or others, possibly unlocking abilities related to the affinity and enhancing the existing powers. Some users may be able draw sustenance from the sacrifice or even slow or stop aging.
Lords of Cinder (Dark Souls series) were people who linked the first flame, sacrificing themselves to keep the age of fire going. Doing so granted them the title of "Lord of Cinder", embuing them with great power.
Gwyn, Lord of Sunlight (Dark Souls) sacrificed himself to link the first flame, becoming the Lord of Cinder.
Should the Chosen Undead (Dark Souls) link the fire after killing Gwyn, he/she becomes the new Lord of Cinder.
Aldritch (Dark Souls III), Saint of the Deep and Devourer of Gods, was forced as a sacrifice to the First Flame for his might, becoming a Lord of Cinder.
The Abyss Watchers (Dark Souls III) sacrificed themselves to link the first flame, collectively becoming Lords of Cinder.
Ludleth of Courland (Dark Souls III) sacrificed himself to link the First Flame, becoming a Lord of Cinder.
Yhorm the Giant (Dark Souls III) sacrificed himself to the First flame, becoming a Lord of Cinder.
In order to fullfill a prophecy, Tai and Matt willingly let themselves be hit by "arrows of light" by Angemon and Angewoman, causing their digimon to warp-digivolve into...
...Wargreymon (Digimon Adventure)...
...and Metalgarurumon (Digimon Adventure).
Rachel (Final Fantasy VI) sacrificed her remaining life and spirit after being briefly revived by the damaged Phoenix esper in order to restore it back to its original splendor.