Dr. Xu's Book

 is a mission item.

Obtaining
Dr. Xu's Book will be sent to the player one day after asking Wuwa about it, during the mission  Dr. Xu's Book.

Usage
Accepting the item will complete the objective, Wait for further notice, and will begin the next objective, Bring the books to Dr. Xu. Bringing the books to Dr. Xu will either complete the mission or progress it to the next phase, depending on the player's conversation choice.

If is sold, the player will be unable to finish the mission.