100 years

100 years. Everyone has 100 years to live. Starting at 100, our lives fall like sand in an hour glass. Our world has 2 laws of life.
1. From the moment your born your life ticks down from 100 to 0. Once you got to 0, you died.
2. If someone were to murder someone, the murderer would have the amount of years the victim had left, subtracted from their life.
That's how life is. Except for when a mysterious character emerges, killing hundreds.
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Years and years pass and the murderer continues to kill. No consequences, No years subtracted. The name "Grim Reaper" has been given to this person. Something that continues to murder and is immortal.