Helldog (ヘルドッグ, Herudoggu)?, also known as Hellhound (ヘルハウンド, Heruhaundo)?, is a demon in the series.
Hellhounds are a variety of supernatural dogs that are demonic or ominous in nature and myths about them can be found across the world. Some of the more common features of Hellhound's are glowing red/yellow eyes, super strength/speed, ghostly characteristics, and others. If one stares into their eyes three times it is believed that the person will die. When the afterlife found in some some religions depict hell as being engulfed in fire, so are the Hellhounds. They often guard entrances to the world of the dead and others hunt or guard treasures/souls connected to the supernatural and afterlife.
In Europe it is believed that seeing a hellhound or hearing it howl may be either an omen of death or the cause of death. Some supernatural dogs were believed to be kind, but their presence is still seen as an omen of death. Garm from Norse myth is a Hound of Hel, while Cerberus is one for Hades.
"A ghost dog that appears in many European countries, especially in the Cornwall region of England. They were guard dogs, guarding the entrance to the underworld, preventing souls from escaping. Hearing its howl is an omen of death."
—Devil Summoner: Soul Hackers 3DS Compendium
Known as Hell Hound
DemiKids Light & Dark
"None have seen and live long enough to tell the tale of this ghostly, evil hound."