Aoi is a Slime Cat, and type of stomach parasite that has acid proof slime on the surface of their whole body. A long time ago, Slime Cats began to stop using their own stomachs because they became parasites, but after a while they lost their own stomach to evolution and are now required to eat half digested food from inside a human host’s stomach to survive. Aoi is about the size of a ping pong ball. Aoi is actually Hatsune Miku who has been transformed into a Slime Cat.