I´m the school beauty´s bodyguard!

Theo, an elite mission-addicted killer, returns home after finishing a task. There, his father gives him a mission of a higher level than any he has ever done before. His new mission... to be a bodyguard! "What a shitty job that is, old man." What Theo doesn't know is that old Lin only wants the young man to be able to recover from his illness...