Servants of Hastur the unspeakable, they are a race of hybrid creatures made of ordinary matter that live in interstellar space. A hybrid who is neither completely crows, nor moles, nor buzzards, nor ants, nor vampire bats, nor decomposed human beings, they can neither be fully perceived nor remembered by a sane person. They can travel through space and carry a rider, but the rider must have something capable of protecting them from the cold and vacuum of space. They can be summoned to Earth to carry out tasks or act as steeds.
Biyarky can be found in the fourth area of the Bomb Shelter. A special conversation can happen between them and Hastur, gifting the Golden Honey item to the party. The Golden Honey prevents all enemy encounters for a while, but unlike the Estoma spell and the Clean Salt item, the Golden Honey will prevent encounters even against enemies of an equal or higher level than the party.
In the new scenario for the PSP port, Tatsuya first encounters these demons in the first part, remarking that he's never seen demons like them before. He realizes that they are servants of Nyarlathotep and fights them.