In the Northern and Southern Dynasties when the State of Chen (A.D. 557-589) was facing its demise1（死亡，终止） , Xu Deyan, husband of the princess, broke a bronze mirror into halves. Each of them kept a half as tokens2（代币，符号） in case they were separated. Soon afterwards, they did lose touch with each other, but the two halves of the mirror enabled them to be reunited.
This idiom is used to refer to the reunion of a couple after they lose touch or break up.
