To end the curse that had plagued his family for millennia, he chose the darkest path.

As the 97th Master of the Demon Slayer Corps, Kagaya Ubuyashiki has always been a gentle and revered leader in the hearts of all his members. However, as the curse increasingly erodes his life, and as he foresees that his daughters will repeat the same mistakes, on the verge of despair, he makes a choice that will shake the world—to make a deal with Muzan Kibutsuji and become the most hidden Upper Moon Zero.

By day, he remains the lord who guides everyone in the fight against demons; by night, however, he is loyal to his millennia-old nemesis. When the truth is revealed on the eve of the final battle, the Demon Slayer Corps' faith crumbles overnight. The former "father" becomes the most despicable traitor, and the Pillars who once swore their undying loyalty turn their blades against each other.

But at the end of this sin-soaked road, does Kagaya hold a trump card that can turn the tide for a thousand years? When wisteria blossoms alongside bloodshed, this game of chess that began with betrayal will finally reach a shocking conclusion.