Abandoned as an infant, Kouyu Li was first adopted by an elderly couple who named him "Kou." After their murder, he suffered a traumatic childhood enslaved before being abandoned as a sacrifice, bound to a sacred tree. Kou Reishin rescued him, bringing him to Kiyou where Reishin's servant, Yuri, provided care. Following Reishin and Yuri's marriage, Kouyu was formally adopted into the Kou family; Reishin preserved his original surname "Kou" by incorporating it into his new name, Li Kouyuu. Driven by a desire to stand beside Reishin and earn his acknowledgment, Kouyu pursued academic excellence relentlessly. At age 16, he achieved the top rank ("Jougen") in the imperial examinations, becoming the youngest examinee in Saiunkoku's history to attain this distinction. Despite his intellectual brilliance, he is profoundly afflicted by a complete lack of directional sense, frequently becoming lost even within familiar environments like the imperial palace, often requiring assistance from others, particularly Ran Shuuei. He also exhibits a short temper, nervousness during public speaking, and vocal distrust of women, leading him to reject numerous marriage proposals from influential families. His professional career began as Vice Minister of the Ministry of Civil Administration, serving directly under his adoptive father, Reishin, the Minister. Kouyu's tenure was marked by diligence, loyalty, and recognition of others' merits. However, his devotion to Reishin manifested unhealthily; he consistently covered for Reishin's negligence by performing ministerial duties instead of reporting the dereliction, prioritizing familial loyalty over bureaucratic integrity. This culminated in Kouyu's imprisonment during the events of the thirteenth novel, accused of abusing his authority as Vice Minister due to Reishin's prolonged absence. Though he lost this position following the scandal, he retained his status as a court official largely through the efforts of Kou Shuurei. Following this setback, Kouyu's career trajectory ascended. He later rose to Secretary within the Department of State Affairs and ultimately achieved the role of Prime Minister (尚書令, Shōshorei). He was succeeded in this role by Hyou Riou Jr. and then by Shuuran, a peasant girl whose life Kou Shuurei had saved. Kouyu maintains complex relationships. His bond with Ran Shuuei is significant; Shuuei frequently aids him when lost, a pattern established since childhood, though Kouyu vehemently denies their friendship. Within the Kou clan, plans existed to arrange his marriage to Kou Shuurei to secure the clan's future leadership. Kouyu deeply admires Kou Shouka, Shuurei's father, even expressing jealousy when Emperor Ryuuki received tutelage from him. His relationship with Emperor Ryuuki evolved from initial frustration over Ryuuki's neglect of duties to one of mutual respect and loyalty, symbolized by Kouyu accepting an iris flower from Ryuuki as a token of trust. His character development involves reconciling his intense desire for Reishin's approval with the gradual realization that Reishin does regard him as a son. This is subtly conveyed through Reishin's choice of the name "Kouyuu," derived from the plum blossom, Reishin's favorite flower. Despite Reishin's outwardly aloof demeanor, his actions, including the adoption and naming, reflect genuine paternal care. Kouyu's journey reflects a struggle between bureaucratic ideals and deep-seated familial loyalty, ultimately navigating these conflicts to reach the highest echelons of Saiunkoku's government.