The four Grandmasters were the Qing Emperor, who had hidden in the depths of the Palace for more than 20 years, Shou Ye Liuyun, the Northern Qi Imperial Advisor Ku He, and the Guardian God of Dongyi, Sigu Jian. However, there was no mention of the people who had not appeared, so there was no way to know.
The Four Great Grandmasters were important figures in " Celebrating Years." They were the Imperial Advisor of Beiqi Kingdom, Ku He, the Qing Emperor of the Qing Kingdom, Sigu Jian of Dongyi, and Ye Liuyun of the Qing Kingdom's Ye family. Each of these four grandmasters had their own stories and characteristics, and they played an important role in the play. Other than the four Grandmasters, there were also some people who had yet to appear, such as Wang Chongyang and Huang Shang. As for these people who had yet to appear, there was no relevant information in the current search results, so it was impossible to give a specific answer.
It could be a rogue Death Eater who has mastered a new form of invisibility spell. This Death Eater might be seeking revenge on those who opposed Voldemort.
The 'unseen messages' could be a mystery that drives the plot forward. For instance, the characters might be constantly searching for the source or meaning of these messages, which leads them to new places and situations. This creates suspense and keeps the readers hooked.
Well, without having read the 'the world unseen novel', it might be about exploring different dimensions or aspects of our world that remain unnoticed. Maybe it delves into the lives of characters who are aware of a world that others are oblivious to, perhaps a world of magic or some other extraordinary elements that are just out of the normal sight of most people. It could also be about the discovery of this unseen world by the protagonist and how that changes their perspective on life and reality.