"Satsui" Doctor Ranmaru (“殺医”ドクター蘭丸) is a manga series written by Kengo Kaji and illustrated by Noriyoshi Inoue.
Dr. Ranmaru might seem a little too lighthearted and lecherous for a doctor, but he becomes dead serious when it comes to the health of his patients. No one knows, though, that he has another goal after hours. He heals his patients during the day, and he helps to repair society by night-- by 'surgically' removing bad people. His usual targets are those that have harmed his daytime patients. After Dr. Ranmaru saves the life of her grandfather, the schoolgirl Maria begins to work part-time at his office. As Maria gets to know Dr. Ranmaru, will she learn his dangerous secret?