"Can't," Lan Zhan says, repeating himself. "I do not know if this is the cost of Chenqing, or what happened during your months here, but I am certain. You cannot practice swords."

Suibian had sealed itself in Nightless City. He knew it when he lifted the blade when they retrieved it. Something had gone terribly wrong, he knew it then. Sealing usually was done when a sword had lost it's master - to death, or worse. He just didn't know what 'worse' was Wei Wuxian.