Even though the Council of Xylon was dangerous, Michael felt that its existence could turn into a great opportunity. Defeating them would increase his prosperity significantly.
He and his people would grow much stronger, and wealthier. Simultaneously, they would have one enemy less to worry about.
'But before I beat the shit out of the Council of Xylon, I should pay more attention to the Soul Grimoire,' Michael figured.
The Council of Xylon hadn't attacked them since their last assassination attempt. They were probably afraid, or uncertain about their next move. That gave Michael enough time to figure out whether he had to upgrade Soul Grimoire to 7-Star or if it would be enough to upgrade Soul Grimoire to a 6-Star Soultrait after inserting dozens of useful sub-Soultraits into it.
