For those who need a refresher there's this (don't read if you don't want to relive Kage's final moment)
The jet black inkiness gradually lightened, turning steel gray, then stormy like a summer maelstrom. Fading further, the gray melted into an ashen hue, like soot from a fire until melting into a lighter shade, reminiscent of the white smoke used to announce a new pope has been chosen. The color intensified, morphing into the same brightness as freshly fallen snow touched by sunlight, until finally settling on a blinding, pure alabaster light.
Everything good which resided inside Kage shone inside that brilliance.
The white adumbration wound itself around Elijah and he felt an unusual sense of comfort from the touch. Then, like a ribbon rippling through a strong breeze, the dazzling brightness circled the room twice as Elijah stood in wonder. He gasped as the radiance punched through the front of his chest, leaving him breathless before exiting out the middle of his back.
Elijah watched in equal parts awe and despair as Kage’s light faded, becoming transparent, before disappearing altogether. He felt something inside of him break. He didn’t need anyone to tell him it was his heart. Something hot, almost spicy-like, was lodged there, and it took a moment before he realized it was Kage. He left a piece of himself behind; a part of his energy, his soul. Something no one could ever take away. In return, he had also taken a piece of Elijah with him. It was a piece of his heart that would forever belong to Kage.