The Worst Best Killer

[Fyi, this is a parody of Teenage Mercenary, a favorite manhwa of mine.]
A month after Jo Na-un returned from overseas, he starts school to further his education, and to experience his lost youth! However, peace is something that won't come very often for this poor fella. From bullies to gangsters to attacks from his fellow mercenaries, he just can't get a break! Luckily, everything ties itself fine in the end. How? Not his skills, as he's actually the weakest of his former mercenary camp. Definitely not his contacts. No, his secret weapon is that he's just lucky as hell!