Main Gods were the peak existences of the world. Still, there wasn't much in common between the Main Gods, as each would have their own unique path.
The phrase "Main God" was actually rather unnecessary, as it was simply a phrase that mortals used to describe the individuals who were the peak existences of the world and had already surpassed the normal limits of a living being's evolution potential.
Main Gods were capable of creating new dimensions by themselves. They were capable of making an entire species go extinct. A single command from a Main God could destroy or establish a country. Main Gods were existences high above the clouds who would act to change the world behind the scenes.