Item from From Blood and Ash by Jennifer L. Armentrout
The rarest bond in Atlantia — two souls connected so deeply that if one dies, the other may follow. Poppy and Casteel are heartmates.
Heartmates are the stuff of Atlantian legend — a bond so rare that most consider it myth. When Poppy and Casteel's heartmate bond is confirmed, it means their souls are literally connected. They can feel each other's emotions with crystalline clarity, sense each other across distances, and draw strength from one another. The cost is equally absolute: the death of one heartmate can destroy the other. It is love made into a law of nature, beautiful and terrifying.