Kou is the second son of the Mukami household. He is an idol in the human world as a side job.
As a human child, he was abandoned in a manhole and never knew anything about his parents or where he had come from. Because he lived in the sewers, Kou would always dream of obtaining the blue sky he saw above. One day, soldiers looking for rebels randomly shot a pair of mother and child in front of Kou as an example to potential rebels. Kou didn’t understand what was going on or knew what the soldiers that found him intended to do to him. When they saw his face, they sent him to the orphanage. Upon arriving there, he received good food, clean clothes, and all the nice things he wasn’t able to have in the sewers. Kou thought of the orphanage as heaven.
Then Kou was taken to a "club." Because of a war that was going on, the country needed money. To earn quick money to fund the war, the club chose beautiful children like Kou from the orphanage and offered them up as merchandise as "entertainment" for aristocrats. Kou was up whipped, cut, beaten, tortured. He was so in-demand that his bruises and wounds didn't have time to heal. Kou didn't want to think that his beating was painful and wanted to believe that he should be happy because he could have nice things.
Eventually, he accepted that the situation he was in was basically hell. In an attempt to stop the orphanage from making him continue as an aristocrat's toy, he lamented that his right eye might never see the blue sky he craved again. He decided to disfigure himself by gouging out his right eye. Unfortunately, that only made the aristocrats desire him more. Kou realized that he made a mistake, and he feared that his situation would only get worse.
Kou tried to commit suicide but found himself unable to kill himself. Soon after, he met Ruki, who called Kou a loser. Kou denied that and tried to kill himself (Ruki even dared him to), but again, Kou was unable to do so, as Ruki expected. Ruki told Kou that the reason Kou couldn’t commit suicide despite desperately wanting to escape his situation was because Kou still had hope. Ruki knew this because he often caught Kou staring at the sky. Ruki told Kou that if he gave up that hope, he would be nothing more than a loser. Ruki invited Kou to come with him if he wanted to be free from his hell.