Kirihito was the boy that died from being caught in an avalanche. So as he died in the avalanche his soul found a way leading to meet the Akura-Ou.
Kirihito decides to let Akura-Ou take his dead body in exchange that he apologizes to Kirihito's mother for fighting with her.
Akura-Ou, also known as Kirihito or the demon king, was an infamous youkai that has been living for at least 600 years. He worked with Tomoe, wrecking havoc to the world of both youkai and humans alike. They were undefeatable that not even the gods of Izumo could defeat their combined power.
That was until Tomoe fell in love with a human woman known as Yukiji. After being captured by the gods, his soul was taken from his immortal body and he was sent to Yomi-no-Kuni and split, his soul sealed into a group of rocks whilst his immortal body thrown into eternal fiery flames.
He lived there for a long time until the soul of a young, recently-deceased, boy named Mori Kirihito came to him and asked him to send an 'I'm sorry' message to his mother because they had a silly argument just before his death. Akura-Ou accepted out of boredom and curiosity and hence took up the boy's body, waking in a hospital room and being hugged by 'his' mother.
After some time, Akura-ou regained some of his followers despite being in Kirihito's body. Two of which were two fox-masked shikigami. He soon decided he wanted to get his original body back from Yomi-no-Kuni.
