When Errillous set out on his own, he knew he wouldn't be able to secure the best territory. He had, however, hoped to rally more than four wolves to his side. And to maintain strong leadership. With Sleet older and more experienced, she was quickly eclipsing him. He was officially the leader, yes, but the pack looked to her during trouble.
And it seemed they should, too. Errillous did not know how to manage a hunt, or prioritize territory acquisition. Sleet knew who should do what in a hunting party, and which lands were more easily taken and which were best. Errillous would not relinquish his role, but he reluctantly stepped back a bit to make way for Sleet. She was the hope the pack needed. Errillous considered becoming her mate, and maintaining relevance that way, only to learn she and Krioss had already chosen one another.
For a few years, Errillous continued to lead. Steadily, though, he felt that his pack didn't really need him. They looked to her for answers. They looked to her for guidance. It was Sleet's pack, in all but name. And so, he left.
