Cores

Cores are glowing spheres of light that replace a saviour's heart. Each core is different depending on their personality and power. The known cores in the series are:
 * Sawyer: A sky blue core that gives her the power of flight.
 * Richard/Rachel: A black and red core that gives him the power of looking into the future.
 * Eve: A red core that gives her the power to shapeshift
 * Glaze: A gray and yellow core that gives him the power of a Dream Watcher.
 * Matt: A light pink and blue core that gives him the power of controlling love.
 * Armin: A dark green core that gives him the power of hypnotism and nausea.

Importance
Cores, since they replace the human heart, are incredibly important for survival. As a saviour grows older, the core shrinks and looses it's glow. As the core shrinks, so does the power. when the core goes out the saviour dies.

A strange thing, however, is that when Matt exchanged his core to save Glaze, Glaze did not inherit his power, nor did he lose his own. This has not yet been explained.

A core can only be created by a saviour, and since Steve was the only past saviour left, he was given the responsibility to create the cores given to the new generation.