Soran had his reasons for not bringing Vivian along.
All the Children of Fear could perceive each other and could find each other when they were at a certain distance. Soran was a little worried about encountering the vampiric demigod, who was now the most powerful Child of Fear and was now a Saint. If they encountered him, they had little chance to win. From this point of view, Vivian was the safest to stay in the outer islands. After all, she was the first Child of Fear, which could be said to be the most wanted target of the vampiric demigod.
With his base now somewhat solid, Soran naturally didn't want more drama.
