A member of intelligence bureau of the special force. She was on a mission to infiltrate the Terrorist group. Her mission was later revealed by another agent when she was trying to look through the confidential documents about ARA and had to flee back to her country. She joined the Counter-Terrorists in hope that one day she could get her hands on the documents again.
Choi Ji Yoon appears in the chapter Chaos as the captain who orders the players to travel through the Rex basement.
She also appears in the Z-VIRUS trailer, investigating a lab. Suddenly, Sting Finger appears and attacks her from behind. She tries to escape and encounters a Venom Guard. Fortunately, she gets an M32 MGL on the ground to defend.