The mythical beast cub is two and a half years old, and the entire dynasty is vying to pamper it.

In the city of Huzhou, two-and-a-half-year-old Yi Yi protects her sick mother, Jiang Wantang, from Liu Fuhai, the son of the local county magistrate, who seeks to force Jiang Wantang into being his concubine. After Liu Fuhai brutally beats Yi Yi, leaving her in a pool of blood, the Empress Dowager arrives with imperial guards. She reveals Yi Yi is the only daughter of Emperor Jing Dongfang Mo, the ruler of the Great Xia Empire, who has been in a coma for months due to a poisonous curse. The Empress Dowager had been guided by the Nation-Protecting Divine Beast, Ancestral Glutton, to find Yi Yi, the only one who can save the Emperor.

The Empress Dowager arrests Liu Fuhai and his father, the county magistrate, sentencing them to death for harming the imperial bloodline. Meanwhile, Yi Yi enters a dream where Ancestral Glutton explains that Yi Yi must aid her father, as the divine beast's fragment merges with her, granting her the ability to absorb and consume Gu worms. Yi Yi recovers miraculously and travels to the capital with the Empress Dowager.

At Zichen Palace, Emperor Jing lies unconscious while court physicians are helpless. Bai Ningbing, a healer from the Divine Medicine Valley summoned by Imperial Consort Liu, removes a small curse-worm but cannot extract the larger mother worm. Yi Yi, possessing divine sight, notices the mother worm and, after pricking her father's finger, lures it out with her blood and swallows it whole. The Empress Dowager and others panic, but Yi Yi is unharmed; the Gu worm becomes part of her, granting her enhanced senses and the ability to consume other Gu worms. Emperor Jing awakens shortly after.

Consort Liu, jealous of Jiang Wantang's existence and the threat Yi Yi poses to her ambitions, attempts to undermine them. She has Jiang Wantang summoned to the Imperial Garden and humiliated, forcing her to kneel in the sun while Consort Liu's maid strikes her. Yi Yi, witnessing this, uses her newfound ability to draw dark energy from her father and release bees that sting Consort Liu and her followers. Dongfang Mo arrives, elevates Jiang Wantang to Consort Xi, and orders Consort Liu to prepare a state banquet as punishment.

Yi Yi settles into palace life, developing a close bond with her father, who is surprised by his own paternal affection. She visits Consort Qi, a frail consort living in Zhi Lan Pavilion, and discovers Gu worms hidden in her chambers. Consort Qi confesses she was a priestess from the Southern Tribes, betrayed by her father, the commander who conquered her homeland, and that she plotted to kill the Emperor using the Soul-Devouring Gu. In a final act of desperation, she attacks with poisoned needles and releases venomous creatures, but Yi Yi consumes the Gu worms and neutralizes the threat. Consort Qi dies from the backlash of her own magic.

Outside the palace, a mysterious figure with silver hair, revealed to be connected to Bai Ningbing, learns of the destruction of his Gu worms and plots revenge, setting the stage for future conflicts. The story establishes Yi Yi as a unique protector of the empire, with her ability to consume Gu worms making her both a savior and a target for those who wield such dark arts.