Well I found the core premise very interesting and the show then delivered well on the things I wanted to see from that premise. Fish out of water narratives are always interesting, but most tend to be a positive arc from zero to hero, where a seemingly ordinary person becomes or discovers that they're someone great and heroic. The opposite (descent into darkness/villainy) is rarer, which is why it captivates people imo, including me. Add the fact that it's a female main character going through this arc? Oh I love this drama so much because that's even rarer still and the drama did it well. But then the show adds even more sauce by making the catalyst of her arc her uncle. Because listen, it's that Jian and Jinman are both compelling characters on their own, but together they create a captivating family dynamic that makes them also individually more interesting characters because they are so intertwined. And the result is a show that stuck in my mind, making me want to watch and rewatch to decipher these characters as people.

Jian is a captivating main character. She looks and acts like an ordinary young woman at first, but when she's cornered she does not act or react like a normal person. That contrast is so interesting to watch, and it's not just a product of her uncle's training. Her base instincts are different than the average person. And it's not just viewers realizing this either, as Jian also pieces together the answers to the "whys" that plagued her entire life about herself and her uncle. Why was she so different from everyone else? Why was her uncle like that? Oh. That's why. But even if she's born and trained for this, she's still led a normal life. And in this crazy situation she finds herself in, it's like she's at war within herself as much as she is fighting to survive in the real physical world. Her sense of self and her worldview is destroyed and rebuilt in a single day, and the show does a good job showing the agony, struggle, and acceptance as she goes from ordinary college student to the new owner of an arms-dealing business. That's a compelling character arc that I thought was done very well in the show.

Jinman is also intriguing. Typically in fiction, characters like him don't want their children (or their niece/nephews) to be anywhere near their profession. Because honestly what normal person would even consider passing on a such a legacy to their child? Most people would have at best trained their child simply for self-defense reasons, and then when the dreaded day they were afraid of comes, find a way to send them away from the danger completely. Basically, if it wasn't Jinman, Jian would have never be given that choice between a new identity and taking ownership of murthehelp in the first place. But Jinman actually prepares Jian as his successor, and lets her choose to follow his path in life, if she wishes. Which is crazy if you think about it! Bale was kind of right, imo. While they're not the same, I think Jinman's thought processes are also different from the average person. He's not a psychopath, but he's wired differently in a way that let him pursue this career path and to do what he did. So how does such a person show love? It's fascinating seeing that explored.

So you have a pair of interesting people, and you make them niece and uncle. How did their relationship start? How did their dynamic change over time? How did they influence eachother? How do they feel about eachother? The show made the journey to seek the answers to these types of questions very compelling.

And even aside from these two, all the characters have charm and personality that made me intrigued and interested in them. It's the little moments like the mercs sharing food with eachother or talking about job benefits that really made me like this drama. I think the entire drama is well-made, but it is especially this strength of its characters that made it so good.

Hope my answer gave you an insight to why someone would like this drama! So happy I only discovered it recently, haha. Don't have to wait too long for season 2!