David is a formal member of a Counter-Terrorist unit.
During a zombie virus incident, he rescued a Female Researcher from being infected by the zombies. He managed to take a short talk with the researcher about the current situation.
At the end of the manga, David shot the female researcher's left leg because she was exposed to the zombie virus. David regretted when he got back and told that the female researcher was holding onto an important confidential data.
He was later infected by Sarah. He tried to kill Choi Ji Yoon but before reaching her, Billy injured him by shooting his head. David didn't die but later a carpet bombing killed him and the other zombies.