Red Demons/Plot

Vaizel 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, Howzer, 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.

Istar arc
When the Ten Commandments are revived and pretend to recover their lost magic power, some Red and Gray Demons are summoned by Melascula in order to collect human souls. One of the Red Demons proposes to carry out his work in Byron, stealing the souls of his inhabitants but is then attacked by Gilthunder, Howzer and Griamore while they were in a road. Combining his powers, the three Holy Knights are able to kill the Red Demon and release the souls he had stolen.

Defensive Battle for Liones arc
During the conquest of the Demon Clan in Britannia, several Red Demons are seen invading kingdoms and killing several knights.

Some Gray and Red Demons attend the Ten Commandments during the invasion of Liones. One of them is destroyed by the Ark of Nerobasta.

During their advance to Liones, Elizabeth and Zaratras meet with a group of Red and Gray Demons, but all are destroyed by Hawk Mama. Then, some Red Demons are called by Monspeet along with other demons in order to sacrifice themselves to load Derieri's Combo Star.

Memories of the Holy War arc (anime only)
Various Red Demons are called by the Ochre Demon in Ordan to fight the Seven Deadly Sins, but all get eliminated by Meliodas's Full Counter.

Prelude to the New Holy War arc
Various Red Demons are with many other demons fighting with the Holy Knights. Some of them are eliminated by Guila, but with she and Jericho are wounded by Blue Demons, a Red Demon pretends to eliminate them with his Purgatory Fire, but is destroyed by Howzer. Thee rest was killed by the Archangel Tarmiel.

New Holy War arc
Various Red Demons are part of the Demon Clan army that is faced by the Holy Knights during the Holy War. Several are eliminated by the knights but the rest manages to release their attacks against them. The rest are eliminated by Diane's Queen Embrace and the Four Archangels's Omega Ark.

During the second wave of the army, a Red Demon is killed by Matrona with a rain of rocks and her Daichi no Kiba. Red Demons tries along with several other demons to devour Elaine when she falls, but all are killed by Ban.