A hundred trillion souls. Roy didn't know how he had proposed this number to Sargeras nor why Sargeras had agreed.
Roy had some guesses in his mind, but they were very vague. With his understanding of himself, he knew that he shouldn't have said this number casually. It should be the amount needed to satisfy a certain condition.
As for what condition it needed to satisfy, was there a need to think about it? It was definitely a condition that the system would fulfill through souls.
Roy guessed that he needed a large number of souls to achieve a certain goal with the system, and this goal happened to be in line with Sargeras's interests, so he agreed to collect souls for him.
