I'm not sure who the author of 'the beast must die novel' is. There are many novels with this title or similar names, and without more context, it's difficult to determine the specific author.
The 'the beast must die novel' might be centered around a conflict where a character or group of characters is determined to put an end to a so - called 'beast'. This 'beast' could represent a powerful and menacing force. Maybe it's a story of a hunt, not just physically but also morally, as the characters strive to vanquish this beast that stands in the way of peace or justice.
The reason why Fan Wujiu said " must die " was because he had once been kidnapped by Zhang Feifei as a hostage. Fan Wujiu couldn't out-scold Zhang Feifei, so he was so angry that he rolled his eyes and blurted out the words " must die ". From then on, Fan Wujiu only knew how to say that he had to die, and he was very good at it. This story was related to the legendary Fan Wujiu of the Black and White Impermanence. However, the literature did not mention why Fan Wujiu said that he must die.