I.V.Y stands for Immortal Vampire Young.

I.V.Y is actually a descendent of a royal vampire family, who cannot burn in sunlight. I.V.Y's mother, who was a mortal, left her at a research lab before vampires killed her. Emily was soon assigned to protect I.V.Y after blood work and other tests were done.

I.V.Y has no clue what she is or how she can destroy all vampires. The zombies are a different story, they jusy follow the vampires regardless. Emily often finds herself looking at I.V.Y as her daughter, who was sadly killed years before the Rise.

Mainly since Emily gave I.V.Y her daughter's hoodie and necklace.