Cheng Guang was telling the truth this time since he indeed did not know.
The power of the Fruits of Path to Divinity, he had not yet fully grasped.
This time, because of the Abyss Demon Emperor's tactics, the Primordial Spirit that had fused with the Saint Dao Fruit suddenly triggered its own instinctual protective response.
Cheng Guang himself merely gave a boost of force, propelling it forth.
As for what specific effects, what kind of power it would have,
Cheng Guang was genuinely not sure.
However,
Considering his current Spirit Dao cultivation and the quality of his Primordial Spirit, even without using the power of the Saint Dao Fruit, merely utilizing some Divine Secret Skills would be enough to defeat some ordinary Sky-Men.
Like the ancient ancestor of the Great Abyss dynasty who had appeared before him, if he confronted Cheng Guang now, it would likely take only moments to kill him.
Only,
