Sgaeyl is the dragon bonded to Xaden Riorson, and she shares a bond with Tairn. That dragon-to-dragon link is what ties Violet and Xaden's inner worlds together.
Because of Sgaeyl's bond with Tairn, Violet can reach Sgaeyl's thoughts, and Xaden's feelings get tangled with hers. The connection runs deep even when the two riders do not want it to — it is a consequence of the dragons' choices as much as their own.
Sgaeyl is loyal to her people and impossible to read from the outside. She watches, waits, and is already there when it matters. Her bond is another reminder that in the Empyrean, dragons are the more dominant partner in most pairings.