The Winter Princess
That voice was undoubtedly Aoi's, the blue-haired elf who was sitting in front of everyone. However, she had spoken so softly that no one in that room had heard. All the others did not react and did not even seem to notice her speech; in the end, there were no other elves or half-beasts in that office.
Elves also have amazing hearing, so it was not impossible for an elf to speak at such a low volume that it was imperceptible to human sound. But this was strange behavior for the head of the events committee, after all, asking Luke to purposely defeat one of his teammates was an odd thing to do.
In Aoi's mind, all the pieces of that board were already falling into place.