When 17-year-old Riyo returns home from school, someone knocks on his door.
As he opens it, he sees a beautiful girl with long black hair standing in front of him.
She only says, "I'm sorry. Please forgive what I'm about to do."
Before Riyo can understand her words, the girl suddenly cuts off his head and disappears.
When Riyo opens his eyes again, he finds himself in a mysterious forest.
He feels like someone is watching him... but who are they?
And how will he become the ruler of darkness in the future?