Oneiros

•Guardian's Oracle: Oneiros, fused with his three brothers, is capable of unleashing this attack, which produces a large explosion around him. The energy released can even destroy souls, thus preventing, according to Oneiros, any reincarnation.

But then Sisyphus of Sagittarius, Oneiros merged with his brothers Having returned to the Sanctuary thanks to Athena, he sends from there the Golden Arrow of Sagittarius, imbued with the goddess's Cosmos. When El Cid perceives the arrival of the arrow, he splits it into four with his cutting technique, and each part pierces the soul of one of the gods that make up Oneiros's body. Before dying, Oneiros tries to kill Tenma, but El Cid prevents him by plunging his hand into his chest, after which both perish in a great explosion.

Oneiros is sent with his three brothers to find Tenma of Pegasus, ordered by Hypnos to imprison his body and soul in the Dream World, where the souls of heroes and kings are imprisoned. After achieving this without difficulty, his brother Morpheus imprisons Tenma in Morpheus, and Oneiros retreats to the Dream World. After the defeats of Morpheus, Phantasos, and Ikelos, Oneiros presents himself to the victors, Tenma of Pegasus and El Cid of Capricorn, explaining that the gods exist in a dimension that humans cannot comprehend, and that he can still summon their souls, after which they merge with Oneiros, resulting in a centaur-like creature. Tenma and El Cid attack the god, but he seems immune to their attacks, and decides to destroy them once and for all with his Guardian's Oracle technique, but the Saints are protected by Nike, who has just arrived in Morphia to rescue the soul of Sisyphus of Sagittarius. To protect Athena from possible attacks by Oneiros, El Cid cuts the space of the Dream World to create a connection with the real world, and with Tenma's help pushes Oneiros through the fissure. Once in the real world, Oneiros discovers three of El Cid's subordinates who had come to help their lord, whom he kills with a single blow, a powerful energy discharge. Tenma and El Cid, aided by Yato of Unicorn and Yuzuriha of Crane, who have just arrived, continue attacking the god, but he survives even after being cut into four parts by the Golden Saints.

Oneiros shares his family's arrogance, although he demonstrates a greater ability to analyze real situations. This is shown when he activates his ability to merge with his brothers from the beginning to fight, because he probably realizes that he alone would not be enough. Oneiros shows that, like his brothers, he holds great respect and loyalty towards Hypnos.

Oneiros has white hair, somewhat long although it can be classified as short, and black eyes. He has a young and attractive appearance, and always wears his armor.