If we want to make clear the function of the ghost seal, we should start with the final ending of the tomb robbery notes. After the secret of Zhang Gulou was finally discovered, his younger brother Zhang Qiling came to Changbai Mountain alone to replace Wu Xie and enter the Tongmen, guarding the Tongmen for ten years. In the final separation from Wu Xie, he gave one of the ghost seals to Wu Xie, and asked him to open bronze doors through the ghost seal to pick him up ten years later. This shows that the ghost seal is the key to open bronze doors, and my younger brother took it by magic.
Where did these two ghost seals come from?
The first ghost seal was auctioned at the Crescent Hotel auction, which was also the one that Wu Xie and others robbed at the Crescent Hotel. Many people say that this is actually a game played by Huo Xiangu and Zhang Rishan. The purpose is to attract Wu Xie through the ghost seal, so as to guide his younger brother Zhang Qiling to find out the secret of Zhang Gu Lou.
The second ghost seal was secretly collected by Huo Xiangu. Later, Huo Xiangu gave it to his younger brother Zhang Qiling, which explains why Zhang Qiling had two ghost seals in his hand when he entered bronze doors.
What does the ghost seal have to do with Xiao Ge and Zhang Jia?
From the above introduction, we know that the ghost seal is the key to open bronze doors, while bronze doors is the secret that the Zhang family has been guarding. The Zhang family is descended from the Queen Mother of the West, so the ghost seal is probably given to the Zhang family by the Queen Mother of the West, which is specially used to open bronze doors. Therefore, the owner of the ghost seal should be the Queen Mother of the West, and later the Zhang clan, in the hands of Zhang Zongzong. But later, because of the misfortune of the Zhang family, the ghost seal was also exiled outside the Zhang family.
Since the downfall of the Zhang family, in order to keep bronze doors's secret, I found the Old Nine Doors, hoping that they could fulfill the agreement. However, because Laojiumen didn't abide by the agreement, it happened that it was Wu Xie's turn to guard bronze doors, and Zhang Qiling, as gay friends, took the role of guarding bronze doors for ten years instead of Wu Xie.
In the process of Xiao Ge guarding bronze doors, Wu Xie successfully found out the secrets of the Wangs and destroyed them through ten years' layout, and then took Xiao Ge out of bronze doors with a ghost seal, so there was the story in Restart.