During a mission, Giyuu got hit by a Blood Demon Art and turned into... a cat? Shinobu checked up on him at the Butterfly Mansion, but she says that there is literally nothing wrong with him and that the effects will go away at some point... whenever that is.

He acts like a cat, he had the energy of a black cat before, but this time he is an actual cat. He really enjoys those feather wand toys and is easily persuaded to do something if you offer him catnip... or simmered salmon with daikon.