Gray demons are tall beings has long scaly arms, sharp claws and feet, and small wings. It wears a lower bottom armor and a sun-shaped helmet with a terrifying face. Standing at 900cm (29'6") in height, they are larger than Red Demons and have slender but muscular bodies.
Gray demons boast a higher intelligence and strength when compared to the red demons. They seem to carry the same low opinions of the other tribes, like the rest of their brethren.
At some point of time, a Gray demon was killed by an unknown individual of great power as it is shown to have died from a large slash wound in the chest. It is shown to have participated in a war between its Clan and the Four Races.
A few years prior to the events of the Kingdom Infiltration arc, its corpse was discovered by Great Holy Knight Hendrickson who studied the Demon's genealogy and biology and conducted countless experiments on its remains.
Kingdom Infiltration arc
After Ban sent Hendrickson plummeting down deeper into the underground chambers beneath Merlin's ruined castle, the Great Holy Knight approached the Demon's corpse explaining to the four Sins Meliodas, Ban, King and Gowther how he obtained and experimented on the demon's body, only to conclude that a Gray Demon was a higher being when compared to its Red brethren. Hendrickson then proceeded to take a blood sample from a Gray Demon's corpse and inject it into himself, resulting in tremendous power-boost, prompting his counterattack by first taking out the Fox's Sin of Greed.
The Seven Deadly Sins: Signs of Holy War
After Hendrickson's defeat, Ban tried to destroy the corpse of the Gray Demon as a form of revenge against the Demon Clan. However, Merlin prevents his assault and claims that she intends to keep it as a test subject.
A gray demon appeared in Byron to collect human souls for the Ten Commandments' replenishment of their magic powers after a red demon was easily killed by the trio of Holy Knights, Gilthunder, Howzer, and Griamore where they, along with Hendrickson who joined them in the fray, had showed its destructive power similar to the latter in that same form albeit in a larger scale.
Despite that, the gray demon was defeated by Hendrickson who used Purge with a single touch with Gilthunder and Howzer assisting, although Griamore had issues with the former Great Holy Knight, concerning about his father Dreyfus' supposed death at the hands of the man who helped them.
Abilities and EquipmentAccording to Hendrickson, the Gray Demon is a being higher than the Red Demon itself and its blood can provide the individual access to its strength, becoming a stable vessel of demonic power.
Gray demons are known to make heavy use of spells that govern over death. Depending on the individual, most of them have power levels in 2700-3200 range. A single mutated variety of Gray Demon is known to exist, and whose power level is said to be immeasurable.
Grey demons also have the ability to fire an explosive, dark energy beam from their mouths.
- Dark Snow「
黒雪Kuroyuki (Dāku Sunou); literally meaning "Black Snow"」: A move that creatures and scatters countless flakes of black "snow". Anyone that comes into contact with the snow will be enveloped in darkness and die instantly.
- Dark Nebula「
暗黒の環Ankoku no Tamaki (Dāku Nebyura); literally meaning "Ring of Darkness"」: A dark void expands outwards from the Gray Demon, completely destroying anything caught within range. The force of the attack was great enough to devastate the surrounding area and incapacitate any caught in its wake.