King Henry was not wearing the suit he wore to the wedding. He still looked like a king in his uniform, just like one of his soldiers, just more decorated. His black hair was slicked back, almost the same colour as his eyes. When he walked into the centre of the room, JongKook quietly stepped to the side, leaving Byul still tied to the chair. 
YongSun could feel her powers growing, she had been desperately reaching for them the second JongKook picked Byul to be in that chair, but they hadn’t reached a level she could use yet, well not effectively. Now that she could see how much JongKook hurt Byul, she reached harder, now that the king had shown up, she was going to need all the powers she could pull. 
Henry looked at his captives with a calculated look. “I am impressed at your attempt to free the princess.” His voice matched what he said, he genuinely sounded impressed. “I was brazen.” A slight chuckle. “I never thought you would try something at the wedding but it was a good distraction.”
No one in the room moved since he walked in, he was just casually standing there as if he was at afternoon tea. “Word has reached me that the camp I was holding some prisoners at has been liberated.” His dark eyes flicked to Byul, making it hard for YongSun to not pull at her chains, her fingers trembling to attack. “I guess I have you and your little friends from the Knight village to thank for that.” YongSun shouldn’t have been shocked that he knew that. “I will admit when I stole those children, I didn’t know who would show up to collect them, the power I felt coming from that village, I never imagined it would be YongSun.” His eyes landed on her, it was as if he was trying to her soul with his gaze. “I didn’t think your father would ever tell you how to unlock your powers.” A sick smile. “What a treat for me.”
YongSun was buzzing with anger, she had to swallow a few times before she could bring herself to speak. “What are you talking about?” 
A snicker. “Did you really think I was making my son marry you for the navy?” He flexed his fingers, his eyes fixed on the black stone ring on his finger. “No silly girl, I was after a different type of power,” Eyes back on her. “Your power.”
“How do you even know about that?” This came from Byul, probably trying to draw his attention from YongSun.
He took the bait and turned. “Ah Yul, I will admit you pulled one over on me, I’d never have guessed you were a woman, or else I would have shoved your head on a spike outside my palace...much like those men who were aiding you.” Byul paled, it must have been outside help she brought with her. “You see this ring has been passed down my family, man to man.” He flexed the black ring. “It has special properties that allow me to do...things. One of those things is to detect great powers. Like the power of the Uju.” 
YongSun should have been scared, she should have been something but angry, but she couldn’t help it. All the work they did, this whole mission, it was a trap set by Henry and they fell right into it. “So you knew what I was.” She said flatly.
Henry shrugged slightly. “Not you specifically, not right away. I felt your birth, I had my men try to trace it but your father bound your powers before I could.” He tapped the side of his head. “Smart man, your father.” He let his hand fall again. “I felt the same source of power almost a year later, but again before I could trace it, it disappeared.” That must have been the Lunarous. “But they weren’t as smart as your father YongSun, they didn’t hide it well enough, every year a little blip of power arose and after almost a decade of looking I found it.” His face turned dark. “Only to have it ripped out from under me at the last minute.” He sounded like he was losing his king's voice, becoming a desperate man. “You were harder to track but the bind your father put on you wasn’t strong enough, powers slipped through and that is how I eventually found you.”
YongSun sat up as straight as she could. “So you think you can get me to use my powers for you?” She felt a smile rise on her lips. “I’d never.” 
Henry smiled as well. “Like I’d leave such a chance open.” He walked closer to her, uncomfortably close. “No YongSun you were never meant to live, you were always meant to end up in this room.” He grabbed her chin rather forcefully. “This is where I take your power and convert it into power for me and my army.” A chuckle. “I will finally be powerful enough to take out the North.” 
So that is what he wanted from Thaiston, the power to crush the North. It was almost so simple that she felt stupid for not seeing it, how had Kedoeron held power for so long, all these generations of being stronger than the South, keeping the North at bay. YongSun figured if he was in such a sharing mood, she’d ask him something. “Then why the prisoners, why attack the Knight, just to lure me out?” 
“No, the Knight has powerful magic, powerful enough to mask the location.