Wondrous Item, legendary (requires attunement by a 1 hour.)
One of two.
Created by a Dwarven mage so he wouldn't have to watch his human wife perish from old age.
The wearers of these amulets become paired for life. The longer-lived party ties their soul to the shorter-lived, extending the latter's life past their natural span, until the longer-lived perishes. Then the two cross to the other side, together.
Notes: Cannot be stolen, broken, or otherwise destroyed once attuned., 1 hour.