In order to tame a Reaper, you must find, fight, and be impregnated by the queen. This occurs with a special attack from the Queen. Within 12 in-game hours, the baby will burst out of your chest. You can collect an item called Reaper Pheromones from the bodies of Reapers, and use them to imprint on the baby. If not, you'll die as soon as it bursts out.

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