They all heard rumors about how the wolf spirits were the collective consciousness of those who had died with peace and love in their hearts. Darius didn't know how Nikita passed away truly, but he figured she had already made peace with her misery before she left her pups in his hands. To meet her among the wolf spirits tonight made him feel a bit too emotional.
More when she came to make her presence known even to Enzo who was just watching them. Darius even had to keep his face down as he walked back to keep people from seeing his tears. It's just that when he took his first step moments after the wolf spirits had vanished, his instincts rang so badly as if the shard was awakened by the imminent danger that came to him.