The Spark of Civilization: the Observer System

(Note, reading this book requires thinking) Many years later, Chen Du was buying water at a convenience store on the street. The girl at the cashier looked up at him and suddenly froze: "Do I know you?" Chen Du smiled and shook his head, then turned and walked into the crowd. The girl touched the non-existent mark on her wrist and muttered "strange". What she didn't know was that her "system" had just popped up the first task: [Help the man buying water remember that he once saved the world.