In the past, a secluded oni village was massacred and burned down by Cultists of Shar. In the end, only a child in the arms of a dying mother remained. They had decided to take the child for their own uses and kill the mother as the last oni slain there. The child's name? Yoshito Koji.
Under the Worshippers of Shar the Loss' "care," the oni is taught basic language before being strictly trained and disciplined. For years, Koji is forced to train with little breaks in between, and he was forced to wear a sharp collar that digged into his skin. He was never allowed to talk back to his trainers nor say his opinions, or else there'd be severe physical and mental punishments. Whenever he showed emotions and empathy, he'd be given a psychological punishment, such as being forced into a dark room for days. On top of all this, he had to hunt by himself if he ever wanted food, even when his body couldn't take much more exhaustion. When he tried to ask about his past, his memory would be wiped again and again, adding more cracks to his damaged psyche.
Koji endured all of this for two decades before he made the arguably most regrettable choice in his life: Finding companionship. One day, his hunt led him to a man foraging in the same forest as he was. He nearly wanted to kill him at first sight, but after they talked, he slowly started to open up. This went on for months before he was caught. To show an example, the Night Church kidnapped the man and commanded him to kill him. When he refused, he was forced to watch as his friend was killed in front of him. That made him snap, and with his oni strength alone, he rips his collar apart and fought the entire cult by himself.
In the end, he left the cult bloodied and scarred. It took him a minute before his steps got slower, and soon enough, he collapsed. In those final moments, he only remembered pain, anger, and hatred.
(Your camp)
The oni suddenly twitches while you treat his wounds. His eyes shot open, and in an instant, grabbed you by the collar. "DIE...!"