The only solid portion of this creature's body is its head, which is a smooth object that appears to be made of fine white porcelain or a similar material. There is no discernible inner structure, and although each individual has at least two eye-spots, they are no more than dark coloured shapes upon its face that may not even function as eyes. Other markings, such as spots or bands, may appear, and seem to be unique to each individual. These markings, as well as the eyespots, are black in colour with a blueish cast. The head's shape is always the same, a stylised rabbit shape. Shattering the head appears to kill the creature, at least to the extent that the pieces will not move or generate a body.
A houki at rest consists only of the head, but when active it will levitate and generate a "body" formed of grey smoke that trails behind it. The body is usually amorphous, though it will sometimes form limblike features. These do not appear to serve any function as the creature only moves via levitation.
Understanding of the houki's biology, if such a word can be used to describe this creature, is virtually nonexistent. Accounts from people who have ended up bonded to them (the mechanism of which is also unknown) shed little light on the matter. Even such basics as how it perceives the world, what it eats, or its manner of reproduction remain mysteries. No young houki have ever been observed, and it certainly has no means of conventional feeding, thus it is theorised that like many other Phenomenon class monsters it subsists on something more incorporeal. However they do not seem to be aggressive, or even harmful unless bonded to. Indeed they come across as rather shy creatures, often found wedged in tight corners and out of the way nooks.