In the energy/elemental-based ecology of the pokemon world of Gods and Demons, pokemon take human beings as trainers because of the greater opportunity for exposure to energy. Even more energy is available through the appropriate bond with a human trainer. However, there are pokemon that can take a human being’s energy instead of depending on it to be freely given, and they are called demon pokemon. Without need to bargain with humans, they are everything humans fear: vampiric, violent, monstrous, and deadly.
Like Auroraboros, “Aricaust” is the species portmanteau given to this demon pokemon in modern times. Traditionally, this pokemon was referred to by the sobriquet 'The Wandering Fire'.
Although it has a fearsome appearance, demon pokemon have long escaped detection through shapeshifting and subtle theft and manipulation of energy. However, the Wandering Fire is prideful, and has come to blows with clan guardians, rangers, and other authorities during its long lifespan.
Aricaust appears in Chapter 16 of Gods and Demons, appropriately subtitled The Gang Fights the Devil Part I. Hoo hoo hoo
(Text is from the third canto of The Inferno.)