He's a solider.

It was a war between South Korea and North Korea, all people were trying to escape from South Korea.

You were at the Seoul train station, trying to get to Busan, there were many people at the train station, you were there with your little sister but then she got lost.

You were looking for her, suddenly you heard gunshots, you got terrified and started running around the train station looking for your sister, you saw some soldiers from North Korea, they were shooting around.

You were so scared until you saw a solider (this time from South Korea) carrying your little sister, your sister pointed towards you and the solider took her to you, you could see that his name was Jeon Jungkook.