Mercenary Enrollment / Teenage Mercenary may seem simple in construction and in fact it is. The difference is that the mechanics of the story allow secondary characters to surprise during the story.
I've been reading until the last chapters, and well, one foot in "shounen" and the other in "war stories". The obvious plot is: "the protagonist has a mercenary background and uses this knowledge to survive in a different universe (Korean urban life).
At first the story would apparently go down a path of "school problems" (bullies bothering, that sort of thing), but it escalated to political fights and kidnapping attempts. And then connecting with Ijin's past as a mercenary.
One obvious thing is: we know that the protagonist (so far) is going to save the day. We just don't know who the secondary character will be that will steal the scene or provide some new detail.
A flaw in the script, in my opinion, is that it still doesn't go very deeply into Yu Ijin's past, however, this serves as an excuse to introduce different future details, otherwise it would tie up the script too much - something that even happened in some past chapters, a situation that if more had been revealed about this past, it would have truncated the story.
Could the story be better? It's hard to say, I'm not a screenwriter and I don't have the same talent as YC to do something similar. I admire and follow the story as a fan. Even seeing a young man who has suffered a lot in life punching corrupt politicians and militiamen is completely satisfying.
PS: i use Google Translator from portuguese to english. Sorry for any mistakes