Ma'am, Your Bodyguard Is a Heartthrob

A commander of the Sky Assault Team comes home after his discharge. He has been through dozens of battles and his body is covered in scars. His younger sister is seriously ill and needs a kidney transplant, and he has no money for it, so he takes a job as the round-the-clock bodyguard of a female tycoon known for being cold. On the job he handles one threat after another, usually in a single move. Soon he is drawn into schemes inside her business, people close to him are kidnapped, and a hidden clan with an old grudge starts moving against them. He has to dig out the secrets behind all of it one at a time, and along the way the tycoon, and more than one other woman, start to fall for him.