Kouya is a young boy who was abandoned by his impoverished mother when he was young, Kouya was raised by a youma he called Okii-no (big one), who called Kouya Chiisai-no (little one). He met Rokuta when they are young and Enki revealed his wish to travel to Hourai, believing that it is a peaceful land and hoping to find his mother. Rokuta named his new friend Kouya, meaning midnight as they had met at midnight. Not wishing to forget his new name, particularly since he had forgotten the name his mother had given him, Kouya asked that Okii-no call him Kouya and began to call Okii-no Rokuta in order to remember his new friend.
Kouya eventually encountered Atsuyu, the governor of En's Baku Province, and was greeted with apparent kindness. In exchange for Kouya's loyalty, Atsuyu provided Kouya with a place to live and a formal education. As a result, Kouya becomes involved with Atsuyu's attempt to overthrow Shouryuu, the King of En, one hundred years into the king's reign. When Atsuyu is defeated, Kouya leaves En and becomes known as Kenroushin-kun ( ,Kenroshin-kun), a heavenly sage tasked with guarding and protecting the people who travel the Yellow Sea. Since then, he has waited for Shoryu fulfill his promise to create a place where Kouya and Okii-no can live in peace.