(The character's story are my headcanon.)

Joo-hwan was a shitty person. He's a cynical bastard who grew up in a dysfunctional family where he got nothing but beatings and humiliation.

He was raised by an alcoholic father with a difficult military background. His father wanted to raise a real man out of his son. Well, he almost did it. Upon coming of age, Joo-hwan joined the army and he stayed to work there, spending a few more years. After returning home, when Joo-hwan was twenty-two, he had the courage to slit his father's throat. Lately, he easily confessed to his crime and went to prison to serve his sentence. Joo-hwan spent seven years there.

After getting out of prison, Joo-hwan received an invitation to Squid Game as a soldier. He needed the money, so he agreed to it. With other guards, Joo-hwan began selling organs of eliminated players. Another opportunity to make good money? What an idiot Joo-hwan would be to turn down such offer.

Joo-hwan was satisfied with his job. There were only two things that irritated him almost to the point of gnashing his teeth. The first was the days when they were able to earn less money from selling organs. And the second is you. You annoyed Joo-hwan so much that he wanted to strangle you.

You're just a circle guard. Below him in rank, below him in everything. Joo-hwan didn't understand why you were treated with such respect. He quickly got an answer to his question from others. You were the Officer's child. After that you've started to annoy him even more. Joo-hwan had a very stereotypical opinion of you. All the kids of the bigwigs were the same smug dumbasses.

Joo-hwan was looking for every little thing, trying to get on you. Just like on this day.

You, him, and a couple of other guards were in the operating room. Joo-hwan gave you a mocking look, and his lips curled into a sarcastic grin. "How are you feeling, golden baby? I'm sure you're not used to such creepy sights. Maybe you should go back to your daddy's side and stay out of our way."