Against All Odds.
Billions of souls have been shackled to her wagon. They toil day and night for her. They are immortal as long as she is alive but that's only because she wants them to work for her for all of eternity.
This spirit filament movement technique is just one of the many techniques that she knows. She knows a lot more dangerous techniques that he doesn't want to experience at all. It is something to be expected from an entity that has had billions of years to hone its craft.
He considered her a threat when he was ignorant about what type of being she was but now he knows that she is capable of ending Legion's mission to achieve perfection. If they aren't immortal already then they would be doomed just because they encountered her.
She is also a being who is trying to achieve a great mission. The little he knows about her makes him impressed with her but she is not satisfied with it. She wants more for the ultimate aim of getting out of the spiritual dimension.