Amidst the chaos of war, the young emperor of the nation of Seikoku, Reiken, proposes to a woman known as the Dark Princess beloved by magical beasts, Setsurin. The proposal is a political offer of peace through marriage. Accepting the contract, Setsurin enters the inner palace as the Dark Consort and becomes one of the four principal consorts of the kingdom. However, she is openly despised and shunned by the court and the other consorts, who view her as an evil consort raised by magical beasts. To protect the fluffy magical beasts who raised her and whom she considers family, Setsurin deliberately wears the mask of a villainous consort and plays the role expected of her, enduring hostility and isolation. Unknown to those around her, she carries a profound secret she cannot reveal. At the same time, the emperor Reiken, who would naturally be a mortal enemy to magical beasts, also harbors a secret of his own that he must keep hidden at all costs.

Despite the harsh treatment, Setsurin navigates palace life while maintaining her facade. She endures constant harassment from the Red Consort, one of the other principal consorts, and faces prejudice against magical beasts from the court ladies during tea gatherings. A fireball appears in the inner palace, causing a commotion, and its true identity turns out to be a magical beast called a fire rat named Hien, complicating her position. When the night of the ceremony to spend time with the emperor approaches, Reiken arrives at her chambers carrying a large amount of work materials, revealing that the famously wise emperor is not merely using work as an excuse but has deeper reasons for keeping his distance. Through Reiken's arrangements, Setsurin is thrilled to learn that her magical beast family will be invited to the inner palace, though the court is baffled and uneasy about inviting their former enemies while a truce is in place. On a day when the families of the other three consorts are gathered, Setsurin catches a cold and is forced by Reiken to rest, despite her desire to greet them as the princess of magical beasts. Later, the Red Consort lures Setsurin and Reiken into a trap, locking them together inside the unused Glass Palace, where the constant bickering pair find their feelings growing stronger in the privacy of the locked room. The Crimson Empress of another kingdom suddenly visits and invites Setsurin to a meal, questioning the significance of the Dark Consort becoming the official empress of Seikoku. When Setsurin falls into a coma, she is trapped in dreams of her sealed childhood memories, revealing the tragic past that befell her and the true reason she was abandoned by humans and raised by magical beasts. Through these trials, the relationship between the seemingly antagonistic emperor and the dark consort gradually deepens, as both struggle to lower their masks and confront their hidden feelings.