A huge man, double the height of a normal person with dark skin, thick arms and legs knotted with muscles and sporting a beard.
2,000 years ago, Anos created the Seven Elder Demon Emperors from his own blood, including Gaios. After Anos's sacrifice, the Seven Elder Demon Emperors co-operated with the Hero Kanon to create the fictional Demon King Avos Dilhevia as a decoy to protect Anos when he reincarnated. Kanon then fused six of his roots with 6 out of the 7 demon elder emperors, including him, and erased their memories. This done so that if they ever came in contact with Anos when he had reincarnated, he will not know about Kanon's plan, since they couldn't lie to Anos.
As part of the Great Demon Sword Training, Gaios and Ydol Anzeo personally appeared to instruct Class 1-2. After being impressed by Anos, Gaios decided to spar with Anos, but due to Anos' cockiness, it became a two-on-two fight. Gaios was effortlessly beaten by Anos, declaring his loss.
At the conclusion of the Demon Sword Tournament, Melheis Boran ambushed the injured Anos and Lay Glanzudlii and brought them to another dimension. Melheis, Gaios, and Ydol planned on overwhelming Anos, but suddenly Gaios and Ydol are both beheaded as Anos stops time on their bodies. Lay was faking his fatal injury and took them out by surprise, Anos and Lay then worked together to defeat Melheis and bring him back to his senses. Anos managed to extract the two unknown roots inside Gaios and Ydol, but they are destroyed by an unknown masked person. Melheis then revives the both of them.
When Avos Dilhevia came back and declared war on Azeshion, Gaios was among the four Elder Demon Emperors who were on Anos' side. They followed him to Eiyan Hill, where Avos' army had built demon king castles to serve as their headquarters. While Anos headed towards the main castle, Gaios and the others stayed to fight the three Elder Demon Emperors who sided with Avos.
When everything was over, Anos teleported everyone back to Dilhaide.
Weapons and Equipment
Ultimate Demon Sword Grajesion: A Demon Sword which split the Neil mountain range in half. The tip of Grajesion was broken after striking Anos' head, but it was repaired by the time of Melheis' ambush.