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.

Knowing of Aria's whereabouts, the Bronze Saints set off to invade the final ruins, followed by Ophiuchus Shaina, who joins them. Before parting, Shaina reveals to Kōga the secret of his origin, as well as Aria's. Inside the ruins, the Bronze Saints face the threat of powerful Silver Saints, while Kōga engages Orion Eden to free Aria. Shaina takes Aria and with her help, they are able to vanquish Mars' dominion over the area. As Mars' power vanishes, the ruins crumble, and the bronze Saints realize Mars' dark power is emerging from the debris of the structure.

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.

Kouga and Yuna reach the House of Capricorn where they meet Ionia and learn from him his reasons for betraying Athena. Kouga attacks the former Headmaster of the Palaestra, but is once again immobilized by his Domination Language technique, and his Darkness Cosmo is brought out. Before Yuna is able to help Kouga keep the Darkness Cosmo at bay, Ionia buries her in a rubble of books, facing Kouga alone. However, after succeeding to repress the Darkness Cosmo in his heart, Kouga awakens his Seventh Sense and finally kills Ionia with the legendary Pegasus Comet Punch.

With Yuna, Souma, and Ryuhou leaving ahead to the Sanctuary, Koga and Subaru look for Haruto in Japan and find, much to their surprise, that he is now a singer in a rock band. Haruto rejects Koga's pleas to return, claiming that to him, his music is now more important than being a Saint. However, during a concert, Haruto watches Koga and Subaru being attacked by some Pallasites, and to protect his friends and his fans, he dons his brand new Wolf Cloth to join the battle.

Eden wanders through the city drawn by a strange cosmo when he meets the Secondary Pallasite Europa and is saved by Seiya. Inspired by the Gold Saint to look for a reason to fight, Eden pursues Europa who was sent in a mission to kill Koga, but has a hard time fighting the enemy until Subaru unleashes an impressive power that was dormant within him.

As Subaru's time is taken away by the Chrono Destruction, Koga, Yuna, Souma, Ryuhou, Haruto, and Eden still have to face the immense power of Hyperion as well as awaken their greater Omega Cosmo.