Every 12 years, mercenaries who possess the highest caliber of brute strength, cunning wit, and deadly precision gather to participate in the Zodiac Tournament. Each warrior bears the name and attributes of one of the 12 animals of the Chinese zodiac. With their pride and lives on the line, they engage in vicious combat until only the victor remains. The 12th Zodiac Tournament begins in a desolate city, devoid of any evidence of the half million people who recently lived there. To raise the stakes, each warrior ingests a poisonous gem, thus setting a time limit on the tournament—and on their life. With one wish for the victor up for grabs, the Zodiac Warriors start their cutthroat battle for survival.

Kazuki Yoshino and Yuuya Niyodo are idols who make up the duo ZINGS. While Kazuki gives his all in every performance, Yuuya views the job as just another means of making money. Yuuya's apathetic attitude toward the fans and inability to take his job seriously causes his manager to give him an ultimatum: unless he starts putting in more effort, he will be fired. Backstage, Yuuya meets Asahi Mogami, an idol dressed in a colorful costume. Asahi would have had a bright future ahead of her—had she not died a year prior. Even as a ghost, Asahi wants nothing more than to perform for fans again. When she finds out that Yuuya does not hold the same passion for the idol life that she once did, she is overcome by a fit of rage and demands that he let her take his place. In a strange twist, Yuuya wakes up to find that Asahi has possessed him and can do what he is too lazy to do himself. With Asahi performing for him, Yuuya thinks he has a ticket to an easy idol life. However, Asahi has other plans. Though she is no longer alive, she wishes for Yuuya to find the ambition that she still has. Together, she wants them to become the best idol the world has ever seen. But can an unmotivated man like Yuuya ever care about anything besides money?

With the initiation of the Patrian civil war came the creation of half-beast, half-human soldiers—a development of the outnumbered Northerners in a desperate attempt to counter the overwhelming Southern forces. Able to quickly dominate battlefields and achieve victory with ease, the soldiers' godlike abilities earned them the name Incarnates. However, as the war raged on, the Incarnates encountered a problem involving the beasts inside them that they were unable to rectify by ordinary means. Once the war was over, mysteries and accounts of the Incarnates submitting to the misfortune of their war days surfaced. Aware of the horrors they faced during the war, Special Sergeant Major and former captain of the Incarnates Hank Henriette becomes a Beast Hunter—those who take the lives of Incarnates who have succumbed to the issues they experienced on the battlefields. After witnessing her father, a former Incarnate soldier, meet his end at the hands of one such Beast Hunter, Nancy Schaal Bancroft resolves to hunt the man who took her father's life. However, Nancy's eye-opening encounter with the Beast Hunter influences her to instead seek the reason behind her father's death and the Incarnates' problematic existence in society.

Alto Goldfilled, a diligent student at the Ortigia Academy of Magic, aspires to become a powerful sorcerer. But he is unable to become one as, despite his excellent grades and strong commitment to his studies, he fails his summoning class. With the threat of repeating a year hanging over his head, Alto tries following an old, worn-out grimoire in a desperate attempt to resolve his situation. To his surprise, he succeeds and summons a powerful demon named Vermeil. As a sign of gratitude for releasing her, Vermeil agrees to become Alto's familiar, sealing their relationship with a deep kiss. Little does Alto know what else he is capable of and what Vermeil's past hides.