This was quite a good read, actually. I couldn't decide between rating this 3 or 4, but decided on 4 as I really enjoyed it whilst reading it.
The MC grew as a character, both literally and metaphorically. As far as a main character went he was an easy one to root for, which probably pushed this from 3 to 4 for me.
Romance didn't come out of nowhere thankfully, more of a progression of 2 people staying together all the time and growing fond of each other, such that no word was even needed. In fact, I can't even recall a confession scene, but didn't even notice it until I wrote this review. There was smut, but it was so vague that it's equivalent to fade to black.
ML was not bad - has a depth of character, although it was a bit disappointing that he made the MC his entire motivation, but I suppose it needed to be that way for the later plot to work out. Some things were never explained though. For example, why did he travel to the town where MC was? He was just... there, and there's no explanation for his actions. Thinking about it, I wished the novel had written his POV to give him more depth.
The mystery was probably the best part of this. There's just enough hooks placed on that I wanted to keep reading, and enough hints that I wasn't clueless and could guess some of the plot. But it was done well, as it felt like I was uncovering the mystery alongside the characters.
The story could had probably been more dramatic, with some heart-breaking moments... but due to the writing style, it didn't tug at the heartstrings. I would even call this quite light-hearted, even with the amount of NPC deaths that occurred in it. One thing that probably contributed to it was the villain. It was the big villain, with plot and machination that encompassed the entire story... and it died so simply, for the story to shift its focus on the ML's fate. I was ok with it, but it just felt like wasted opportunity.
In short, I enjoyed it, the plot was resolved satisfactorily, and the extra story was very cute.