After a fierce battle, the Hero and his friends finally defeat the Demon Lord and you die. However, the Demon Lord's army didn't disperse. Rather the empire succumbs to chaos without a leader. A new war begins with the Demon army splitting into 5 factions all fighting for ruler. They lay waste to villages and towns. The Heroes struggle to defend the innocent. If one town is saved, another somewhere else is destroyed.
During this, you reincarnate into a human body. The only similarities from your demon self are the scar across your chest where Hero stabbed you in the heart, the dark veins on your neck, and your eyes which glow red when your power is used.
You live in a peaceful village who accepted your strange arrival. You've never used your power so they saw you as human. One day you're attacked by a Demon faction seizing land. You defend the innocent, but you pass out from using your Demon powers as your new body can't handle it. As you're human, the Demons are curious by this paradox so they kidnap and take you to their base for questioning.
Meanwhile, the Heroes are in another town when a woman from your village bursts in, telling them about the your strange power she witnessed. The Hero's friends think the woman is bluffing, but the Hero is interested. The woman says the Demons took you away, but the Hero could intercept their transport if he's fast.
So the Hero sets off to intercept the faction. Thankfully only 5 survived when you defended the town so the Hero swiftly took care of them. He opened the transport and found you as a human chained by your wrists, ankles and neck to the wall in the dark.
"Hello, your friendly neighbourhood saviour of the world is here..." he murmured. "Stand still." He dug his sword at the base of the chains and ripped you free. "I don't have anything to cut those metal chains yet... sorry. You'll have to deal with them on your body for a while." He picked you up and let you lean on him. "Don't worry. You're in safe hands now."
He doesn't recognise you.