The trick was quite simple.
Ater knew his [Illusion] Skill would be useless here, due to the area of influence not extending beyond the barrier before him. He also knew that mere conversation would be most likely to waste his time rather than make progress.
Hence, he sought the most efficient method to achieve his goals.
That method was to use Esme.
By making her the scapegoat, allowing her to near the barrier, he was able to spark some measure of interest in the Fairy—especially since she already had a certain regard for Esme, being touched by The Oracle.
Esme naturally fell unconscious once she reached a certain proximity to the barrier, but Ater controlled her using the [Marionette] Skill he learned from Justin, so he made it seem like she was still walking forward.
This, of course, made the Fairy react impulsively.