The central plot of "Twin Star Exorcists" is driven by the prophecy that Rokuro Enmado and Benio Adashino will give birth to the Miko, the exorcist destined to end the thousand-year war against the Kegare. The first major twist reveals that the Hiinatsuki Tragedy, which caused Rokuro's deep trauma, was orchestrated by Yuto Ijika, Benio's estranged and powerful twin brother. This inextricably links the pasts of the two protagonists and establishes Yuto as their shared nemesis.
During their final confrontation with Yuto in the anime's first arc, Benio loses her legs and has them replaced with Kegare-based enchanted limbs by the Basara Kamui, making her a physical parallel to Rokuro and his corrupted Kegare arm. This event marks the anime's primary departure from the manga. The subsequent anime-original arc introduces Sae, a young girl who is revealed to be a branch of the Ame-no-mihashira, a massive tree that is the source of all spell power. Her existence is tied to the Dragon Spots, which are causing instability between the human world and Magano.
The ultimate antagonist of the anime is revealed to be Abe no Seimei, the legendary first exorcist, who exists as a being of pure Yang energy. His goal is to absorb all Yin energy and create a world without individuality or conflict, effectively ending humanity. He created the Kegare as a byproduct of this flawed plan. In the final battle, Rokuro and Benio discover that their purpose was not just to birth the Miko, but to become the perfect fusion of Yin and Yang themselves. With the help of Sae and spell power from all over the world, they achieve a perfect Resonance, defeat Abe no Seimei, and restore balance to the world, choosing a future where they can be together out of love, not just prophecy. They confess their feelings for each other in the final moments, bringing their romantic and action-filled journey to a conclusive end.