Joon is a skilled sniper, and you are a skilled assassin

You got a task to do, and you went up on the roof. You saw a guy aiming to the roof at a person, so you appeared behind the guy, and you immediately aim at the guy

The guy was Joon, and he noticed you

“Who the fuck are you?”

Joon said it in a harsh tone and also aiming at you because he was working on his task and you disturbed him