A powerful demon from a shadowy realm, once known as the Golden Beast, grew weary of the darkness and longed for a world filled with light, family, and friends. Defying her origins, she tore through a summoning gate and was reborn as a human baby in the Holy Kingdom of Talitelud. The second prince welcomed his newborn daughter, Yulucia, as a blessing, unaware that she is a devil in disguise. Now revered by the kingdom as the prophesied Saint, Yulucia must hide her demonic hunger beneath an innocent facade while navigating a world she has always dreamed of.

The story follows Yulucia as she grows up in the royal court, learning to balance her genuine love for humanity with the dangerous darkness still residing within her. She is eventually assigned four attendants by her father, but rather than being competent guardians, the group is lazy, selfish, and greedy, which Yulucia finds perfect for her purposes. At her fifth birthday party, held at the castle by decree of the king, she finally meets her devious older sisters, who attempt to play pranks on her only to be met with the little devil's laughter. Later that night, she receives an intriguing invitation to a moonlight tea party from a mysterious figure known as the silver princess, whose scent of blood fascinates Yulucia.

As Yulucia grows older, she enrolls as a student at the Academy of the Magical Arts. Despite being the sole princess of the royal family, a candidate for the Saint, and possessing immense wealth and power, she struggles to make friends and finds school life quite lonely. She faces constant harassment from multiple fronts, including her jealous older sisters who continue to scheme against her and the Hero's party, who refuse to give her any respite. When she receives an invitation from Duke Kapell, a noble known to resent her family, Yulucia recognizes it as a trap. However, this constant barrage of human malice does not break her spirit. The joke is on her enemies, as their negative emotions and malicious intentions turn out to be one of her favorite sources of sustenance.

The narrative explores Yuluciais dual existence as both a revered holy figure and a creature of darkness. While she may have escaped her shadowy origins, the past is never far behind, and neither is her hunger. As whispers of her true nature begin to spread and dangerous schemes close in around her, Yulucia must protect the bright human world she has come to cherish while satisfying the demonic cravings that threaten to expose her secret.