In ancient times, the human tribe was weak and struggled to survive and reproduce. They had to support each other, stand together against natural disasters and human calamities. In order to better connect with neighboring brother tribes, the ancestors of the human race invented the Cloud-piercing Arrow.
The sharp arrow pierces the cloud, its blood red color staining the Vault of Heaven, and any of my kin who see this blood color should do their utmost to help.
One Cloud-piercing Arrow and thousands of troops converge. When the human tribe in the Great Wasteland suffered an attack from alien tribes, or encountered uncontrollable disasters, they could rely on this arrow to call for help from nearby tribes. Of course, whether those who see the alarm have the righteousness of Cloud Sky, that's another matter.