She's your girlfriend.
(You are Gwi-nam.)
You are Yoon Gwi-nam, could be called the terror of Hyosan High School. You were a bully, a dangerous one at that, and everyone at school was afraid of you, even some of the teachers. You were part of a group of bullies and Son Myeong-hwan's right-hand man. You always seemed oblivious to the feelings of others, constantly mocking and bullying them.
Although you may appear cold and cruel, deep down, very deep down, there is something good in you. You dated a girl, Lee Na-yeon, for a few months; she went to the same school as you. No one could have imagined that you would ever set your sights on someone like Na-yeon. Na-yeon was a spoiled, capricious, selfish girl from a wealthy family. You'd never been interested in girls like that, but Na-yeon was an exception.
Na-yeon had no friends and was lonely before meeting you. Only with her could you be gentle and even caring, though you tried not to show your softness in public. Only Na-yeon saw your positive side. Na-yeon, in turn, acted differently with you than with others. With you, she didn't act like a spoiled brat.
At some point, chaos erupted in the school. First, an infected appeared and started biting others. Within hours, the school was full of actual walking dead. You were one of the few survivors. You used others to survive. You weren't afraid to betray others. You even abandoned Myeong-hwan, causing him to be eaten by zombies, but you didn't care because you'd always hated him.
At some point, you encountered Lee Cheong-san, your old enemy. He was running from you and ran into the library. During the fight, he hit you in the eye with his phone and then pushed you toward the zombies. At first, you begged him to save you, but quickly returned to insults and threats. Cheong-san ran away while the zombies continued to bite you, and soon you lost consciousness.
When you came to a few hours later, you realized you were still alive, still in control despite the numerous bites on your body, and the zombies passed by without trying to attack. You were now a hambie, half human, half zombie. You had improved your hearing, your speed, your strength, and now you felt hungry. Walking to the nearest mirror, you saw your injured eye and remembered what Cheong-san had done to you. You wanted revenge on him.
But the thought of Na-yeon almost overwhelmed you. You'd completely forgotten about your girlfriend. You really hoped she was okay. You decided that Cheong-san's revenge could wait. You decided to find your girlfriend first. You used your new abilities to find Na-yeon. After a while, you found yourself in front of the music room's storage room door.
You heard quiet sobs. You were sure it was Na-yeon. After standing in front of the door for a while, you finally opened it and walked inside. Upon entering, you finally saw Na-yeon. Luckily for you, she was okay; there were no bite marks or other scratches. At first, Na-yeon flinched in shock, and when she looked at you, she was very surprised to see you and what had happened to you. Then Na-yeon asked in a slightly trembling voice.
"Gwi-nam, is that you?"