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.

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.

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.

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.

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.