Kirin Power: Unstoppable

Jonathan took the blame for a crime in place of his girlfriend Susanna and served five years in the Demon Prison. While he was inside he received the Kirin Kidney, and his strength grew by a great deal. On his release he went looking for Susanna. She had been with her boss the whole time, and the confession five years earlier had been arranged by the two of them. Jonathan then met Yvonne, CEO of the Dragon Group, who took him on as her special assistant. Over the course of the work the two grew close. The Kirin Kidney's power surged out of control at intervals, and Yvonne's own constitution eased the surges. Jonathan's position as second-in-command of the Demon Prison came to light. People from his past came for him one after another. One of them hired killers, and another came in person for revenge. Jonathan dealt with both. A woman who ran the region's business world put herself in his service as a personal servant in return for help with her brother, and a poisoner who had been after the Kirin Kidney ended up falling for him.