My Bodyguard is Four-foot-two

My Bodyguard is Four-foot-two manga summary: On the cusp of becoming a middle-aged man, Qin poses as a private investigator during the day while running an illegal body-modification drug business on the side. This seemingly "tranquil" lifestyle is about to be shattered by the arrival of a mysterious boy. Ian, the boy, claims that from now on, he will protect Qin, who'd lost both his parents at a young age. Faced with his new pushy, pint-sized roommate slash "bodyguard". Qin will  cooperate or...