Scythe.

About Scythe

Scythe is a 2016 young adult novel by Neal Shusterman and is the first in the Arc of a Scythe series. In the far future, death, disease, and unhappiness have been virtually eliminated due to advances in technology, and a benevolent artificial intelligence known as the Thunderhead peacefully governs a united Earth. To replicate natural death and keep population growth in check, a group of humans known as Scythes are mandated to kill.