Why did the secret king change the protagonist in the second part?

Klein completed his mission and became a true master of mystery.

In the first novel, Lord of Secrets, Klein has three tarot cards (Justice, Hermit and Baita) by participating in the tarot club, and successfully completed his mission as the protagonist. At the end of the story, he reached the peak and became a mysterious master in the true sense. This change is not only a natural and reasonable development of the story, but also allows readers to witness Klein's gradual growth from an ordinary person to a world guardian and decision maker. The appearance of new characters as messengers further expands the world outlook and plot content of the novel, presenting more diversified and colorful story clues.