Eden sees his own darkness as Aria is constantly being used by Mars without the power to do anything about it, before being confronted by his parents about his destiny for the new world. Accepting whatever punishment that would be suitable for his errors, Eden allows himself to succumb to his darkness. Meanwhile, tormented by her own darkness of being used as an instrument of destruction Aria resolves to use her Light to protect those who need her, in doing so she reaches both Eden and Kouga from their darkness and all reach the Core of Darkness. Aria then along Kouga...

Learning of Souma's defeat, Eden leaves the Sanctuary in order to find Aria himself. He eventually manages to track down Aria, who is accompanied by Kouga and Yuna. After easily defeating Yuna, Eden and Kouga have their long awaited fight. However, the Orion Bronze Saint easily dominates the battle despite Kouga's best efforts. Not wanting to see her friend hurt, Aria allows Eden to take her away.

Kōga is worried over the disappearance of Athena and frustrated for his failure to protect her and his mentor Shaina. Kōga is determined to master his Cosmo to rescue his goddess. Kōga departs to improve his mastery over Cosmo, later meeting Sōma, the Lionet Bronze Saint, who teaches him about the elements of Cosmo. Eventually, Kōga and Sōma are greeted by the challenge of Mantis Ordykia, one of Mars' henchmen, who puts their command over Cosmo to the test, an experience that strengthens their newfound friendship.

Kōga arrives to the Palaestra, guided by Bear Geki and his disciple Sōma. There he is greeted by Saint apprentices, who first approach him with hostility. Also, Kōga meets Aquila Yuna, the young female Saint, who teaches him about his constellation and about the code that guides Saint women.

The Saint Fights tournament continues. Geki and Kōga bond more while the former teaches the young Saint about the mysteries of Cosmo, and reminisces about his defeat at the hands of Seiya years ago. In the tournament, Yuna triumphs over Delphinus Güney, and Kōga and Sōma are pitted against each other in battle. As both are driven by strong motivations, Kōga draws more strength from the memories of Geki to narrowly achieve victory over his friend.

After Sōma's fateful battle, the Bronze Saints reach the famed Lushan fairylands in China, and are rejoined by Dragon Ryūhō. Shortly afterward, the teens suffer the assault of the ferocious Perseus Mirfak, who turns them to stone, with the exception of Ryūhō, who barely manages to defeat Mirfak, repeating the miraculous feat his father performed years ago, against Perseus Algol. Continuing their journey, the Saints tresspass the Lushan waterfall with the help of the Libra Gold Cloth, only to be greeted by the challenge of a mysterious young man named Genmu, who takes the Libra Gold Cloth as his rightful heirloom, as he reveals himself to be the Libra Gold Saint.

After his victory over Sōma, Kōga senses a familiar Cosmo approaching, which he recognizes as Athena's. Rushing to meet her, to his surprise, he finds not Athena, but a frail, fearful young girl, whom Capricorn Ionia reveals to be Athena's true self. Ionia also reveals his true allegiance, to Mars, and reveals their plans to a shocked Kōga. After defeating the young Saint, Ionia leaves with the young girl, not before laying waste to the Palaestra, leaving it in ruins. Hours later, Kōga awakens in Mars' Saint Prison, to be greeted by the mysterious Wolf Haruto.

The malevolent entity known as Mars invades Sanctuary, accompanied by Capricorn Ionia and the young girl they claim to be the new Athena. Mars then completely obliterates the millenia-old Sanctuary, replacing it with his very own fortress. Meanwhile, Kōga manages to escape the Saint Prison with the help of Wolf Haruto, and after rejoining the other Bronze Saints, they set off together to invade Mars' headquarters, to rescue the young girl and to learn about the whereabouts of the true Athena

Kōga and friends continue their trek to take Aria to safety, when they're surprised by the attack of Hound Miguel. Overpowered by the merciless Silver Saint, the lives of the Bronze Saints are saved by the timely arrival of Andromeda Shun, the Saint of legend. Shun takes the youngsters to his village to rejoin Ryūhō, afterward they're once again attacked by Miguel, whom they manage to defeat after a fierce battle. Later, the young Saints leave Shun's village to continue their mission.

Eden takes Aria away, and Aquila Yuna and Pegasus Kōga resume their journey, demoralized by their failure to protect their friend. Along the way, Yuna and Kōga separate, meanwhile Eden and Aria reminisce about the happy days they shared during their childhood. Kōga later meets a young man who first mocks his weakness, luring the teen Saint into a fight. Kōga later realizes the man to be the owner of an immense Cosmo, and turns out to be Cygnus Hyōga, one of the legendary Saints who protected Earth from great menaces many years ago. Hyōga manages to teach Kōga that to reach the true potential of his Cosmo, he must first believe in himself. After learning Hyōga's lesson, Kōga rejoins Yuna and both resume their way with renewed resolve.

After the defeat of Kouga at the hands of Harbinger, the remaining Bronze Saints engage him in battle, meeting with utter defeat. Harbinger reminisces about his difficult childhood and what drove him to a life of violence, to become the strongest and eventually a Gold Saint. Managing to recover after witnessing the defeat of his comrades, Kouga attacks Harbinger with a single blow imbued with all the power of his Cosmo. Much to his surprise, Harbinger emerges unscathed and his comrades have vanished.

Koga arrives at the Gemini Temple. He and Ryuhou join forces in order to defeat Gemini Paradox. Despite their best efforts, the two of them are outclassed by the more experienced warrior, especially when her darker half comes out to fight. Incensed by Paradox's selfish nature, Ryuhou manages to awaken the Seventh Sense and pull out a desperate win at the last minute. Ryuhou and Kouga the head off to the Cancer Temple.

Athena Saori watches over peace on Earth from Sanctuary and over young Kōga, until an invader causes commotion when he tries to kidnap Athena and the baby. Kōga is saved from certain death by the timely arrival of Gold Saint Seiya, who engages the mysterious invader, who reveals his identity as Mars. A new conflict begins as Seiya and Mars battle for the fate of Kōga, who years later, determined to live his life as he sees fit, challenges Athena.

The young Bronze Saints bravely invade Mars' Babel Tower, and succeed in rescuing the girl he claims to be Athena. She reveals to Kōga that her name is Aria. Sensing a threat approaching, Kōga dispatches Yuna along with Aria to avoid being recaptured, and together, the young Saints try desperately to buy time for their escape by facing the seemingly invincible Leo Mycene. In their darkest hour, a memory of Seiya deep in Kōga's heart brings them hope.

Yuna arrives with Aria to a small town. In Babel, Mars send Sonia (the Highest Martian), The Crow and Miguel of the Hound (Silver Saints) after them. Miguel guides the bad gang to the town where Aria and Yuna are in a church. Aria is left hidden and Yuna goes to fight. Right when Sonia is about to kill Yuna, one martian arrives asking Sonia to go back to Babel for a meeting of Mars with all the Saints. It is revealed that she killed Soma's father. She leaves and the Crow is beating Soma and Yuna. Koga save them and help Yuna to deliver a fatal blow on Crow. In Babel: Yuna, Soma, Koga, Ryuho and Haruto are blamed for Santuary destruction and taking Athena apart. So all the Saints are looking for them.

Kōga and his friends continue their trek escorting Aria, until they come to a enormous whirlwind blocking their way. Meanwhile, Mars reveals his plans for his Tower that he deems the new Twelve Zodiac Temples, to his daughter and son, Sonia and Eden. A moribund Athena is also revealed by Mars, held hostage inside his tower. The young Saints decide to brave the whirlwind, managing to find a way inside it with the help of Yuna's command over wind. The traitorous Musca Fly tries to steal Kōga and Yuna's Cloths, only to be defeated in a fierce battle. Weary and alone, the young Saints find a new light of hope in the Pegasus constellation, which reveals a message from the legendary Seiya: "To you, I entrust Athena!"

Yuna arrives at the House of Cancer, and she is greeted by the deathly atmosphere of the gates of Praesepe. The guardian of the House, Cancer Schiller, engages her in battle, reminiscing about his past and motives for his allegiance to Mars. Aiming for Yuna's utter defeat, Schiller tries to break her morale by toying with her psyche, having Yuna fight her deceased friends Arné and Komachi. Meanwhile, Kouga continues his battle with Harbinger. After another clash between the two Saints' greatest techniques, Kouga heads towards the exit. Admiring his determination, ...

Upon arriving at the next temple, Haruto and Souma are confronted by Virgo Fudo, a gold saint whose cosmos surpasses that of all the Gold Saints in the earlier temples. Yuna, Kouga, and Ryuhou join the battle in time to save their friends from a crushing defeat. But even the combined powers of the five Bronze Saints is no match for Fudo. When all hope seems lost, Eden arrive at the last minute and protects them from one of Fudo's techniques.

Eden takes over the fight against Fudo after blasting Kouga and the others out of the Virgo Temple. Following a desperate battle, Eden manages to defeat the Virgo Gold Saint when he awakens the seventh sense. At the same time, the other Bronze Saints attempt to use the opening he gave them to go to the Libra Temple. Unfortunately, they are confronted by Tokisada, the new Aquarias Gold Saint and the man who killed Haruto's brother. His apparent ability to control time makes him a powerful adversary and Kouga is defeated with little effort.

Kouga finally reaches Mars' location, determined to stop him. As the War God deflects his attacks and counterattacks, Eden arrives in time to save Kouga. Mars then reveals to the true story from the days when he was known as Ludwig, a normal human who sought revenge for the death of his beloved wife, Misha. He deflects Eden's attacks before removing his mask, revealing himself as a human no longer.

Sending Kouga ahead Eden awakens his Seventh Sense and challenges Mars, immobilizing him with his Cosmo. Eventually, while Kouga struggles to retrieve Aria's staff at the top of the Sanctuary, Mars breaks free and grievously wounds Eden, temporarily defeating him. Pursuing Kouga, Mars easily shrug off any attack from the Pegasus Saint until Eden finally catches up to the two. Bringing their Cosmos to the limit, Kouga and Eden finally defeat Mars together and have Ludwig return to his senses. However, just as Ludwig is about to retrieve Aria's staff to prevent Earth's ...

After infusing the Darkness Cosmo in Kouga's body, Amor finds out that he was betrayed by his sister from the beginning and swears to kill everyone including her, knocking out Eden in the process. Meanwhile on the Earth, Kiki, Harbinger, Fudo, and Genbu use their Cosmos to send Kouga's friends to Mars. As he finally reunites with Saori, Kouga is overcome by the Darkness Cosmo and possessed by the God of Darkness, Abzu, who kills Amor in one single blow. As the possessed Kouga now proceeds to kill Athena with his own hands, his friends try to have him return to his ...

Ryūhō, the son of the legendary Bronze Saint Dragon Shiryū returns to the Palaestra after a short absence. The young Saint apprentices are subjected to a strict training to master their Cosmo element. Kōga is later forced to battle Ryūhō in an intense element-to-element duel.

The Bronze Saints reach a snow-covered land, which causes Yuna to reminisce about her days as a Saint apprentice and her mentor, the kind Peacock Pavlin. Sensing her mentor near, Yuna rushes to her encounter, only to realize Pavlin's allegiance is to Mars. Disciple and master engage in a fierce duel, later Yuna realizes it was Pavlin testing her, as her mentor reveals she is truly loyal to Athena Saori, and informs Yuna she is still alive and being held hostage by Mars. As Yuna prepares to rejoin her fellow Bronze Saints, both female Saints are surrounded by traitorous Silver Saints. Pavlin stays behind to cover Yuna's escape, seemingly losing her life.

After briefly mourning the death of Aria, the Bronze Saints prepare to enter the Twelve Zodiac Temples. They are greeted by Aries Kiki, who explains the situation and how they are to proceed. Taking him for an enemy, Kouga attacks Kiki, to what he responds by restoring the Pegasus Cloth and also revealing to them the crucial secret of the Seventh Sense. Realizing Kiki is not an enemy, Kouga proceeds to the Temple of the Golden Bull, where he is challenged by its guardian, Taurus Harbinger, and a deadly battle ensues. Meanwhile, Kiki restores the remaining Cloths, and stays behind the teenagers, to battle alone against a large group of Martians.