This article is about Kirihito before he was possessed. For Kirihito taken over by Akura-Ou, head to Kirihito (demon).
After his soul left his body he found himself in Yomi-no-Kuni, the underworld. He found Akura-Ou's soul and asked him to pass an "I'm sorry" message to his mother to relieve his regret for having had a trivial argument just before he died. Akura-Ou agreed to send him his message out of boredom and tiredness from being in the darkness.
He was a cheerful, optimistic, and hopeful boy, even after his death. He also cared for his mother very much as he did not wish to leave without saying sorry for their fight just before he died.
He willingly let his body get possessed so he could say sorry to his mom, unaware that Akura-Ou would continue using his body as a vessal to live in the human world.