The Demon Warrior’s real name is Akira Minamoto. He has an ancient curse set upon him because he’d betrayed someone very important in his past. He is chained up and left to die by the one who he betrayed. Although he doesn’t exactly remember who the person was, he knew that he couldn’t regret his decision. 
Akira’s curse can only be broken by the breaking of a seal, summoned after breaking his coin mask. He is much older than he looks, due to the demonic being sealed inside him.