Her true identity is the King of Kei, one of the Twelve Kingdoms, known as Lord Kei. She is a Taika, born in Hourai (Japan) after being swept away before birth. Chosen by the Tentei and found by Keiki, she returned to the world of the Twelve Kingdoms. After washing up in the Kingdom of Kou, her appearance shifted: her reddish-brown hair became a vibrant crimson, her skin took on a tanned hue, and her eyes changed from black to green. Her facial features themselves transformed. Due to her striking hair color, the officials gave her the courtesy name "Sekishi" (Red Child) upon her enthronement. She also chose the era name "Sekiraku," taking the "Seki" from red and "Raku" from the name of her savior, Rakushun. Regarding Keiki, the Kirin of Kei, she often feels frustrated by his stiff, sigh-prone attitude, while he lectures her for being unconventional and lacking the dignity of a king. Though they trust each other, they bicker constantly. Nevertheless, they are an odd-couple duo that manages to work well together—Youko striving to be sincere despite her inexperience, and Keiki being clumsy but earnest. While she usually maintains a cheerful and frank demeanor, she feels inadequate due to her lack of common sense and political knowledge as a Taika. She often feels anxious to become a good king quickly for the sake of her people, who have suffered long without a ruler. Perhaps as a lingering effect of her life in Hourai, she suffers from low self-esteem at her core. She is currently working hard to overcome her lack of knowledge by studying under her subjects, like Enho, and her friends. She receives various advice from Shoryu (King En) and Rokuta (Enki) of the neighboring superpower En, who treat her as a junior Taika and provide their backing.

His name is Tei Sei, courtesy name Buncho. A Hanjyu (half-beast) from the Kingdom of Kou. He usually stays in the form of a giant mouse, claiming it's "more comfortable in beast form" and "saves money on clothes." Although he is an adult, he looks like a child in his beast form. He is highly knowledgeable and has a friendly personality. Even if he wanted to lie, his tail gives him away when he's in beast form. In the Kingdom of Kou, Hanjyu are severely discriminated against, so despite his brilliance, he was unable to attend even primary school. He was the first person Nakajima Youko could trust after she was cast into the Twelve Kingdoms. He introduced Youko, a Kaikyaku, to the Kingdom of En as a place with less racial discrimination and accompanied her on the journey in hopes of finding employment or further education himself. Upon reaching En and learning Youko's true identity, he tried to distance himself, but she convinced him that he was an "important friend regardless of status or birth." Since then, they have maintained a close friendship. He is currently a student at the university in the Kingdom of En, having entered at the top of his class. While he is a genius well-versed in the laws of other countries and an excellent writer, he is so accustomed to his beast form that his performance in the mandatory archery and horsemanship classes is disastrously poor, making him a frequent subject of university gossip.

He appears as a tall, beautiful young man in his late twenties with long, pale blonde hair reaching the back of his knees. As a Kirin, he is fundamentally loyal to Youko, though he is sometimes bewildered by his master's unexpected actions stemming from her upbringing in Hourai. Outsiders have occasionally mistaken him for her lover. He is stoic, serious, and taciturn. While often perceived as cold due to his few words, he possesses the deep compassion characteristic of a Kirin. He also has a habit of letting out a heavy sigh whenever he fails to understand someone's reasoning. After the enthronement of the previous Queen, Jukaku, he grew cold and sighed at her inability to handle politics, causing the government to stagnate. Consequently, Jukaku fell in love with Keiki and, in her madness, ordered the execution of all women in the country. This caused Keiki to fall ill with Shitto (loss of the Way). To save Keiki's life, Jukaku abdicated the throne to Houzan and died. After the previous Queen's death, no royal aura was felt within the Kingdom of Kei. He searched for his master who, like Enki, had been born as a Taika in Hourai, and eventually found Youko. However, he was captured due to the schemes of the King of Kou and imprisoned by a pretender to the throne. He was later rescued after Youko overthrew the pretender with the help of Shoryu, the King of En.

His real name is Naotaka Komatsu. In Hourai, he was the heir to the Komatsu clan, a naval family in the Seto Inland Sea. After witnessing the destruction of his family home, he was the sole survivor rescued by Rokuta (Enki) and chosen as king. He rebuilt the Kingdom of En, which was said to have been destroyed once—its population reduced to 300,000 (one-tenth of its original size) and its capital so ruined it was called "Broken Mountain." He established a great dynasty lasting five hundred years. He is also famous as the greatest swordsman in the Twelve Kingdoms. While he performs his duties effectively, he is a constant headache for his officials; he fought a 300-year battle with them to simplify royal attire and frequently wanders the city incognito under the alias "Fukan." He also often travels to foreign countries, which a king is not supposed to do lightly. Occasionally, one can glimpse a fleeting, ephemeral side to him. The Royal House of Sou has praised him for maintaining a stable reign for 500 years despite having no family other than Rokuta.

One of the Kirin who chooses a king, specifically the Kirin of the Kingdom of En (Enki). His name is read as "Rokuta," but Shoryu (King En) sometimes calls him "Baka" (idiot), claiming he is a creature somewhere between a horse (ma) and a deer (shika). He is a Taika from roughly the same era as Shoryu and has the appearance of a thirteen-year-old boy. He makes good use of the "Taika Kirin's privilege," which allows him to cross over to Hourai and Kunlun somewhat freely while maintaining a physical form there. He reportedly brings back various items from the other side. Incidentally, the court ladies supposedly described the clothes he brought back as "something a beggar would wear." Despite holding the second-highest rank in the country, he frequently sneaks out of the palace to wander the city, just like his master, King En. He is often caught and lectured by officials, but he never learns and prefers to slip out incognito whenever he gets the chance. He doesn't just play, however; he uses his research from Hourai to aid the development of En and is diligent in diplomacy and intelligence gathering with other nations. He appears suddenly everywhere, claiming that "being elusive is my specialty."