Based on context clues and my shallow grasp of kanji and Chinese/Japanese terminology, I think 使役 might be referring to animal familiars, but I'm not 100% sure.
thank you for the chapter and a vampire with 8th grade syndrome that's adorable good girl tier material.....although in all fairness it was a perfectly natural response on Izayoi's part to run off like that after Aoi did such a bold power move like a double lewd handholding with someone she just met. It just shows poor Izayoi is a pure and wholesome girl who wasn't expecting to suddenly reach third base with a practical stranger. I hope later Aoi at least takes responsibility and takes Izayoi to vampire prom or something of that equivalent.
Wouldn't surprise me if the animal club was about draining them for their blood. It's a typical vampire trope to prey on animals instead of humans if possible.