Dragon Devil

Y/n L/n, A boy who found himself in hell one day. He walked through hell for a few hours before coming to giant door with flames buting around it. The door opened before Y/n came face to face with a giant golden dragon. The dragon thought of Y/n as a foolish human before being surprised as Y/n showed no sign of fear. This intrigued the dragon which made them propose a deal with Y/n in the form of a contract, they would allow Y/n to use their power in exchange for his left arm. Once Y/n agreed to the contract, his left arm became a black and red gauntlet. After awhile, Y/n began training with the dragon devil's powers as he defeated countless of devils in hell even the Darkness Devil before claiming the title of "The Strongest Dragon Vessel". What happens when that Dragon Devil goes back to the human world and meets a couple of Public Safety Devil Hunters.