Scythe (Arc of a Scythe series)

In a future where disease has disappeared and people do not otherwise die, professional Scythes carry out sanctioned killings known as gleaning. Teenagers Citra and Rowan are selected as apprentices even though neither wants the role. As they learn why the vocation exists, they are placed in competition with one another. Only one can become a Scythe’s apprentice, and the winner’s first assignment is to glean the other, turning their training into a struggle for survival.