A martial arts prodigy spent his whole life in exchange for the happiness of a beautiful woman in the rest of his life. After spending his whole life, he became a demon because of a chance. The woman was hit by an arrow and fell into the cliff to save him... After a hundred years of practice, he climbed to the top of the demon world. During the peak showdown with the previous demon king, the powerful demon power tore the space and was sucked into the space crack. He fell into the modern world. He was seriously injured in the battle with the demon king and was taken home by a girl... For the girl, he embarked on the path of being a gangster.