I'm having a very shitty headcanon, Kayn was expecting a daughter from Zed and for fear that Zed would discover and despise him, he fled from the order and had her and raised her for a few months away from there, since Shieda left the order and most of them considered a traitor he was no longer under zed's guardianship, kayn was just someone else from Ionia and he was persecuted (The kinkou maybe idk order) penalized for his crimes (They executed him lol, he was very weak and no longer wanted more conflicts to live in peace with her baby), but before he abandoned his daughter hoping she could survive, she was adopted by peasants who raised her and made her join the Kinkou, something ironic since she does not know her true origins