The story takes place in the ancient kingdom of Hokugi, within a vast imperial harem filled with thousands of beauties. Wang Karin, a trainee palace maid, has one simple dream: to make friends. However, her father, Wang Kou, is a notoriously vicious and corrupt high-ranking official who is feared throughout the court for his brutality and rumored assassinations. Because of her father's reputation and her own intimidating appearance—sharp downturned eyes, jagged teeth, and dark circles—everyone she encounters screams and runs away. Karin is utterly alone, spending her days in tears. One rainy night, while sobbing by herself, a small boy offers her an umbrella. That boy is the young emperor, Gyousei, the only male in the harem and a frail, lonely child who ascended the throne at age ten after his older brothers were assassinated. Touched by his kindness, Karin resolves to protect him. During the winter sacrifice festival, she discovers that an assassin has infiltrated the harem to kill the emperor. Using the comprehensive assassination techniques her father drilled into her, she eliminates the threat. Karin realizes the emperor has no allies and is constantly targeted by forces vying for the throne. She dedicates herself to guarding him with her deadly skills, even as she longs for a peaceful life. As she navigates harem conspiracies, she befriends a few fellow maids, earns promotions, and reunites with her long-absent older brother, Wang Sei, during a promotion exam that culminates in her single-handedly quelling a rebellion by spreading rumors that her father would massacre the rebels. She also uncovers the truth about her late mother, Wang Ken, who was reviled as a wicked woman but in reality sacrificed herself while protecting children caught in power struggles. This revelation deepens Karin's understanding of her family's burdens. The main narrative arc revolves around the power struggle among three powerful women controlling the harem: the Empress Dowager Kenken, the Consort Ga Taihi, and the Grand Princess Kouki. The Empress Dowager, fearing the emperor's growing independence, orchestrates an assassination attempt during a ritual sword dance, which Karin foils. Later, the Empress Dowager frames Karin's family during the Wutong feast, forcing the entire Wang clan to unite in a desperate counter-scheme. As punishment for exposing the plot, Karin is sentenced to hard labor at the detached palace, where she wins over the other prisoners and reunites with the emperor, who is studying there in seclusion. The young emperor Gyousei grows from a passive, sickly boy into a determined ruler who vows to create a world where no one cries. Karin, despite her fierce appearance and deadly competence, remains socially awkward, emotionally fragile, and desperate for ordinary friendship. Her family, including her terrifying father and her twelve older brothers, are revealed to be deeply loving and protective beneath their fearsome reputations. The story balances dark palace intrigue with warm family bonds and Karin's earnest, often clumsy efforts to live a tranquil life while being impossibly skilled at killing.