Reishin Kou holds the position of Minister of Civil Administration and leads the Kou clan, a role he took over nearly fifteen years ago after his elder brother Kou Shouka left the main estates. He deliberately allows outsiders to believe his younger brother Kou Kurou is the clan head to preserve secrecy. Married to Princess Kou Yuri, the previous Emperor Shi Senka's half-sister, they are the adoptive parents of Li Kouyuu. His immediate family includes his niece Kou Shuurei (Shouka's daughter) and brothers Shouka and Kurou. Reishin presents a cheerful, easy-going, and often childish exterior, prone to playing tricks on officials and excessive behavior like overwhelming Shuurei with medicines during her illness. However, he possesses a calculated, secretive nature described by his close friend Ko Kijin as crafty, coolheaded, and coldhearted. This duality fuels intense protectiveness over family, especially Shuurei, manifesting in violent jealousy towards her suitors—like throwing a fan with lethal intent at Emperor Ryuuki. He concealed his familial relationship to Shuurei for years, fearing she might blame him for replacing her father, yet insisted she call him "ojisan" (uncle). Professionally, Reishin achieved second place in the Imperial Exams, earning the title of Bougen. As Minister, he oversees the Ministry of Civil Administration where his adoptive son Kouyuu serves as Vice-Secretary. His tenure ended in resignation and house arrest after false accusations of manipulating Shuurei's exam results, a scandal that triggered a Kou clan work stoppage crippling the government. Though exonerated, he was later stripped of his position entirely in connection with Kouyuu's imprisonment and returned to Kou province. His relationships are marked by devotion and obsession. He harbors profound respect and loyalty towards his elder brother Shouka, secretly aware of Shouka's identity as the assassin "Black Wolf" and working to protect him, particularly regarding Shouka’s guardianship of the exiled prince Seien (Shi Seiran). Reishin's fixation on Shuurei borders on irrational; he once expressed a desire to marry her himself until Shouka reminded him he was already married. His marriage to Yuri originated in childhood love, though she initially disliked him. He persistently refused to acknowledge her engagement to Shouka or her disguised identity as "Yuzuriha," eventually forcibly marrying her while she was half-conscious after ransoming her. Despite his detached behavior, Yuri is considered his ideal partner and credited by Shouka for raising Kouyuu well. Reishin adopted Kouyuu ostensibly to "share his brother's experience" after Shouka adopted Seiran, but Shouka reveals Reishin genuinely views Kouyuu as his own son. Reishin maintains a significant friendship with Ko Kijin, supplying him with handmade masks and being one of few who tolerate Kijin's unmasked face. He also shares a long-standing camaraderie with Imperial Exam top scorer Tei Yuushun. Culturally skilled in playing the biwa, the Kou clan's traditional instrument, he reserves this talent exclusively for his wife Yuri.