Sargeras's corruption of Argus's Star-Soul had been completed, but Argus's Star-Soul had not fully awakened and remained dormant.
This so-called dormant state merely meant that the Star-Soul could not manifest before others in the form of a Titan body. Argus's consciousness, however, could already engage in limited soul communication with many living beings.
How should one put it? Sargeras had clearly "force-ripened" Argus's Star-Soul to achieve this!
If a planet nurtured a Star-Soul, then before that Star-Soul fully awakened, it resided within the planet's core. Wrapped in a thick crust, even the fluctuations of its sleeping soul could not spread outward. Thus, even demons, creatures highly sensitive to souls, could not detect whether a planet possessed a Star-Soul while standing on its surface. In other words, while a Star-Soul slumbered, its existence was difficult for the outside world to notice. Only by delving deep into the planet's core could one accurately determine whether it had nurtured a Star-Soul.
This was also why the Old Gods could only choose planets at random to descend upon, and why they had to take root underground after parasitizing them. Their appearances revealed nothing; only personal investigation could verify the truth.
Sargeras—or rather, the Titans of the Order Pantheon—were different. They possessed special means of sensing their own kind, so compared to other races, they had a much easier time finding Star-Souls.
Dormant Star-Souls were difficult to detect, but Star-Souls beginning to awaken were another matter. Argus's Star-Soul should originally have remained asleep for much longer before awakening, but Sargeras had used a special method to force-ripen it, causing Argus's Star-Soul to enter its awakening state early. Thus, at the very instant Sargeras completed the process, Roy and every demon across Argus sensed the incomparably immense soul consciousness beneath their feet!
The presence of that