Cavern Guy has the Death Note

.. any action you take which results in a PERSON dying prior to the percribed time of death in the main book of fates is yours to use or trade as you wish. Caveat: only some people have "fated" times of death and most of these are "persons of destiny" (i.e. people whom have some advantage gifted upon them to success or fame). Most regular people are so close to death at any given moment that keeping track of them is pointless.

Death dealers can influence fate by lending a person life years or helping them "cheat" death, if but for a time. This is generally frowned upon but not regulated, as it is some of the only entertainment afforded such beings who otherwise don't give a duck.

Example: you were supposed to be killed by a car at 5 pm today. Instead, car owner has heart attack & wrecks before killing you. Fate must now apportion life span from driver to death dealer whom killed them, but also to you (with you taking first taste). If death dealer then kills you, they get that as well. What sucks for normal people is, you only benefit if you are a death dealer or associated to them (contracted at end of life to become DD). NOTHING buys you more days whilst alive.