I was rewatching episode 14, where Guo Changcheng writes with it at Wang Xiangyang's request and Wang Xiangyang says that it's an heirloom of his and he only uses it to bring good luck to his shop. Since the brush can also apparently give people power who didn't have any before and create energy storage cells, I'm wondering if maybe the brush's power is that whatever it's used to write becomes reality?