The crystallization in Selphira. The way her system responded to Orion's beam. The difference between that and what Ren saw when he looked at the crystals already formed.
Something in the comparison was giving him the outline of something that might work.
But the knee that had been holding Selphira gave, and then the second knee followed, her body responding to the accumulated weight of everything it had received, the hours in the ruins, the climb up the stairwell, the tunnel, the ceremony hall, all of it presenting the final invoice simultaneously and refusing to continue negotiating with her will about the terms. The crystal network spread through her as it would through stone that had found its natural fault lines.
The strange internal way of working of it, the way the crystal metabolized the energy was the only thing that let her keep receiving it at all.
Ren's eyes had been opening, incrementally, across the last several seconds.
