Shiryu, Hyoga and Shun are about to jump into the hole leading to the Underworld, but Dohko stops them, warning them that only Specters will be able to reach that world alive. He also tells them that they must reach Arayashiki, known as the Eighth Sense. Shaka and Athena had reached this sense by being as close to death as possible, to reach the Underworld alive. Dohko and the Bronze Saints, thanks to their previous battles, awaken the Eighth Sense, and land in the Underworld. Seiya has made it as well, reaching the Eighth Sense beforehand and encounters Shun. Now they must find Saori and give her Cloth to her. Seiya and Shun reach the Acheron River, and see dead people who lived their lives in apathy and aren't allowed to cross the river. A boat comes with a Specter, Acheron Charon, who guides dead people across the river. He begins to fight the Saints, but offers them a ride in exchange for money. Shun offers Charon a golden pendant, something he has had since he was a baby. Even though Charon says it isn't enough, he gives them a ride. At the halfway point, Charon knocks Seiya off the boat where he is being dragged to the bottom by dead people who tried to swim across. Shun saves Seiya and he attacks, breaking through Charon's Rolling Oar defense. The Specter falls into the water, asking for help since only he knows the way to the other side. Shun helps him, but Charon attacks Seiya with Eddying Current Crusher. He then attacks Shun, but looks at his pure eyes, being aware of his pure heart and stops the attack, thinking he might end up in Elysium, a paradise for people chosen by the Gods. Thankful to Shun, Charon returns him his pendant and agrees to take him and Seiya to the other side, on the condition they settle the score. Charon explains the contents of the Underworld, consisting of 8 prisons, 3 valleys, 10 pits, and 4 spheres. Seiya and Charon continue their battle. Since Seiya has seen both of Charon's techniques, he is victorious, killing the Specter with his Meteor of Pegasus. Hyoga, Shiryu, Dohko and Kanon have also made it to the Underworld, but are in different parts of it. Seiya and Shun reach the First Prison, the Palace of Justice.

Seiya and Shun reach the First Prison and encounter Markino, a skeleton that leads them to Balrog Rene, who judges the dead and sends them to their appropriate hell. Markino is then killed by Rene, using his Fire Whip, because of him not being quiet. Rene proceeds by showing Seiya his past crimes during his life with Reincarnation. Seiya is shown childhood memories, and the opponents he has defeated. He then tries to explain his actions, but Rene ignores him and sends him to the First Valley of the Sixth Prison, where people who have use violence against others in their lives boil in a lake of boiling blood. Shun rescues him, however Rene notices something strange about Shun. Shun tries to justify the actions of humanity, but is sliced to pieces with the Fire Whip. Rene is then scolded by Hades for cutting his body. In panic, he searches for the body, but Rhadamanthys appears, pointing out it was an illusion. Seiya and Shun are fine, wondering what happened. Rene discovers who made the illusion, Gemini Kanon, who wanted Rene to lead him to Hades. Kanon then destroys Rene with no difficulty and confronts Rhadamanthys about why he defeated Aiolia, Mu and Milo so easily, because of a barrier at Hades' castle that lowered their strength to 1/10. Seiya and Shun arrive, but Kanon attacks them, reminding Shun to be stop being sentimental, in order to save the innocent. He then tells them to go find Athena. Rhadamanthys attacks Kanon, but he counters with the Imperial Satanic Illusion to control him and kill Hades. He is interrupted by Specters who tell Rhadamanthys that Pandora wants to see him. As the Judge leaves, Kanon destroys the lower Specters with Galaxian Explosion.

Seiya and Shun reach the Second Prison and encounter Cerberus, the three-headed Watchdog of Hell. Sphinx Pharaoh, guardian of the Second Prison, feeds dead people who were greedy, to Cerberus. The beast tries to eat Seiya, but is defeated by both him and Shun. Suddenly, Lyra Orphée, a legendary Silver Saint just as powerful as the Gold Saints, appears. Pharaoh says that Orphée came to the Underworld willingly and serves Hades. Pharaoh uses Balance of Curse with his harp, about to tear out Seiya's heart. But Orphée plays his lyre and attacks with Stringer Nocturne, defeating the Bronze Saints. He then goes to a garden, visiting his beloved Eurydice, confined to a rock. Seiya and Shun, who survived the attack, arrive in the same garden and encounter Eurydice. She asks them to please help Orphée. She explains that back on Earth, Orphée and Eurydice lived as a couple, in love with each other. However, she was killed when she was bitten by a poisonous snake. Heartbroken, Orphée went to the Underworld, pleading with Hades to revive Eurydice's soul back to Earth, playing his lyre. Pandora lets him know that his request was granted, but on one condition: both must not look back, not even once, until they reached the surface. Wanting to keep Orphée in the Underworld to play his lyre for Hades, Pandora has Pharaoh trick Orphée with a mirror, reflecting a light resembling the sun's light. Orphée turned around, but Eurydice's lower body was confined to a rock. He decided to stay with her since then. Eurydice asks Seiya and Shun to take him back to Earth. Orphée ignores Seiya's request for help to defeat Hades, but Pharaoh appears, taking the Athena Cloth. After learning that Pharaoh reveals he is the reason Eurydice is bound to remain in the Underworld, Orphée prepares to fight Pharaoh.

Orphée plays his Death Trip Serenade, making Pandora and the three Judges fall asleep. Before he can attack Hades, Rhadamanthys strikes Orphée, knowing he would betray them. Seiya and Shun emerged from the trunk unscathed and attack the Judge. Hades appears, wearing Shun's pendant, and Hades's face looks exactly like Shun's. Orphée attacks with Stringer Fine, with Hades seemingly destroyed, but it is revealed to be a fake body. Rhadamanthys strikes Orphée's heart, ordering him to awake the other Judges and Pandora. Orphée, dying, tells Seiya to attack them both while he holds Rhadamanthys. Seiya awakens his Eight Sense and attacks with his Meteor of Pegasus. As Orphée dies, he entrusts the Bronze Saints with Athena. Rhadamanthys survives the attack, but Shun begins to act like Hades and his hair turns red. Seiya tries to snap him out of it, but Hades has taken over his body. Rhadamanthys attacks Seiya, defeating him. Both Seiya and Orphée's bodies are taken to the frozen hell in the Eighth Prison, Cocytus, where the dead who have committed crimes against the gods, are buried up to their heads. Pandora and the Judges awaken, and Hades sits on his throne. The Judges find it hard to believe the God of the Underworld used to be a Saint. Hyoga, Shiryu and Kanon arrive at a swamp in the Fourth Prison, guarded by Lycaon Phlegyas. Hyoga and Shiryu are defeated by him, but Kanon kills Phlegyas with his Galaxian Explosion. He takes the raft and the unconscious Saints with him to the Fifth Prison. At the Eighth Prison, Pandora tends to Hades' wounds from her spear, trying to find them in the trunk. She then calls him her younger brother.

Shiryu and Hyoga recover as they reach the Fifth Prison, where the dead are forever burning. They encounter Kanon as he kills a giant Specter. Rhadamanthys arrives and tells the Saints about Seiya's defeat and Shun becoming Hades. Kanon tells Hyoga and Shiryu to continue while he fights Rhadamanthys and gains the upper hand. Suddenly, Aiacos and Minos come to kill Kanon and attack with their Galactica Illusion and Cosmic Marionattion, respectively. However, the strings from the Cosmic Marionattion are suddenly cut, releasing Kanon. Just then, with his Final Cloth, Phoenix Ikki arrives. Kanon tells him that Shun is Hades, but Ikki doesn't believe it. When Ikki hears Pandora's name, though, he remembers that when he and Shun were children, Pandora, as a child, tried to take Shun from him, saying his body belongs to Hades. He hadn't seen her for years after that. Ikki is distracted and gets attacked by Aiacos. He then gets up, in tears, realizing Shun is going to sacrifice himself. After accepting his challenge, Aiacos sends Ikki flying with his Garuda Flap twice. On the second time, however, Ikki manages to knock down Aiacos. Back on Earth, Eagle Marin encounters a mysterious, but familiar young girl.