Red Demons

The Red Demon  was a member of the Demon Clan, who (probably wanting the water of the Fountain of Youth) burned the Fairy King's Forest. After it fatally wounded both Ban and Elaine, the former drank the water and then quickly defeated the demon with his new-found immortality.

Appearance
It was a very huge and fat creature, with a clown-like face, sharp claws & teeth. Its two horns had rings that were alternatively colored black and white. Its blood vessels were visible on the neck.

Personality
It was a wild and vicious beast, going on rampages with reckless abandon to achieve its goals.

History
This Red Demon was a part of the Demon Clan, which was sealed for eternity after losing to the Goddess Clan allied with the Humans, Giant Clan and Fairy Clan in an ancient war. However, it somehow escaped the seal.

Bandit Ban
Just as Ban offered to find Elaine's brother, the Red Demon suddenly appeared, probably to steal the Fountain of Youth, and started burning the Fairy King's Forest with its purgatory fire. Ban, immediately instructing Elaine to take the cup of the fountain and escape, began attacking it and successfully removed its heart. However, it did not die, since demons possess more than one heart, and then fatally wounded both Elaine and Ban with its claws. After Elaine made Ban drink the Fountain of Youth, he becoming immortal, quickly and angrily defeated the demon.

Sometime after it was killed by Ban, its corpse was found by some knights who were sent to investigate the Fairy King's Forest's destruction, including Hendrickson, who also discovered a power enhancing quality of the demon's blood, and that its blood could transform compatible living beings and draw out immense power after witnessing crows mutated after they ate its flesh. This quality of its blood has been used by Hendrickson to secretly increase the abilities of many ordinary Holy Knight apprentices, many of whom were considered as failures. The apprentices were called the "New Generation" with the kingdom unaware of their new abilities' origin. Hendrickson also experimented on himself as well, resulting the obtaining of Demon powers and Hellblaze.

Byzel Fight Festival arc
Twigo and Jericho are brought to the cave, where the Red Demon's corpse is hidden by Guila. After receiving explanations about the qualities of its blood, the two decide to drink it due to their desires for greater strength. Twigo, however, explodes due to being incompatible; Jericho remains fine and survives after ingestion.

Kingdom Infiltration arc
As Great Holy Knight Dreyfus leads a strike group of Holy Knights (Gilthunder, Hauser, Guila and Jericho) into Merlin's old castle, Helbram expressed worries of what would happen if Dreyfus find the Red Demon's corpse beneath the castle before encountering Diane underground.

Later, when the five of the Seven Deadly Sins battle Hendrickson at the ruins of Merlin's old castle, Ban discovers the corpse after being sent flying into the wall by the Great Holy Knight. Recovered, Ban questioned the Druid's acquisition of the corpse and then assaulted Hendrickson in full force, that sent him flying into the wall. The wall collapsed to reveal the chained demon's corpse with the Sins' shock and Hendrickson laughing in confidence. Hendrickson reveals how he came by that corpse and used it to make countless experiments on the Old and New Generations and himself, boasting of the vast powers he had gained before attacking the Sins again with Ban taking the blow and revealed to the Great Holy Knight that he was the one who killed it 20 years ago before pummeling him. After Ban smashed Hendrickson far deep underground, the Fox's Sin of Greed destroyed the demon's corpse with his nun-chunks.

Abilities and Powers
The Red Demon was shown to be an immensely powerful being, capable of mass death and destruction. In its battle against the immortal Ban, it demonstrated great strength to withstand and persevere through a barrage of lethal strikes, leading to a battle of endurance between the two. Its claws were strong enough to greatly wound Ban, who only survived the onslaught due to the immortal regenerative powers gifted to him by the Fountain of Youth.

As a demon, it retained the characteristic biological features of its species, including possessing multiple hearts and the ability to create unnatural black wings that it could use to fly. Its most catastrophic power was the ability to breathe "Purgatory Fire" (煉獄の炎, Rengoku no Honoo) from its mouth. This unholy, black flame was so destructive it could even burn the Fairy King's Forest to the ground; a forest that could not be burnt by natural fire. It was also capable of firing destructive beams from its eyes, which it used to fatally wound both Ban and Elaine before they had time to react.

The Red Demon's blood possessed the unusual trait of unlocking great power within certain individuals. Those compatible to the blood receive unnatural power and ability upon consumption, shown by their eyes changing color to an eerie black. Incompatibility to the blood leads to rapid swelling of the body, ultimately causing the individual to explode and die.