My Second-Grade Apprentice Thinks the World Is a Game

Gu Huai just wants to be an ordinary social worker, get off work on time and lie down on weekends. Until a girl from the mountains squatted in front of the convenience store and called "Master" when she saw him. She pointed at the sensor light: "Illumination!" Pointing to the elevator: "Teleportation array!" Pointing at the router: "Information Energy Tower!" Gu Huai: ... This is a city, not a world of immortality. The girl nodded: I understand, it's all disguise. She asked seriously: "Master, when are we going to save the world?" Gu Huai looked at his demon core that had been broken for five years and fell into deep thought. What's even more troublesome is that she is humming a nursery rhyme: "The day when the rusty sword is reforged, when the devil awakens." What is this girl's background?