To be honest, this is something I've been thinking about since the beginning of this novel. There are four things in particular (if I mention anything wrong with the plot or the story itself, please forgive my bad memory):
1- The way James manages to travel to the other world is rather... vague. He's walking through the forest and suddenly a mysterious portal appears out of nowhere and absorbs him, and that's it. If it had been something more, I don't know, mystical, it could have been better (like: while trying to leave the forest, he hears a wolf howl, gets distracted thinking about how dangerous yet strangely alluring it sounds, so he slips and falls into what appears to be a hole. When he opens his eyes, after a brief faint, he finds himself sitting in a cave, then follows luminescent runes and finds the exit, sees the world, and when he turns around, there is no entrance to the cave, leading to the subsequent events. In the future, after returning to his world (if he does return), he could find himself in a small landslide instead of a hole that led to a cave where he initially slipped, allowing the author to use the excuse of "it was all a dream," but with the possibility of knowing it was real (like a handkerchief or souvenir from that world that he has in his backpack)).
2- I don't find it very believable that, even without knowing he's in another world, James would just walk into someone else's house as if it were the most normal thing in the world. At least give him a reason for doing that, like he actually sees the beings from that world, panics, and has no choice but to enter the house because these "terrifying" creatures were approaching.
3- How is it possible that he understands both the language and the writing of that world? Normally, and at the very least, other protagonists in other novels have grappled with this from the beginning. A brief mention and a possible explanation (like: "it's thanks to MAGIC") would add more depth to the story and explore the potential uses of this "possible" ability. For example, at first, he might be amazed that he can understand and read the language of the normal books he's given, but then he doesn't notice the difference and understands when he hears and reads another language or dialect, and of course, he can at least speak them. The simplest explanation is MAGIC, at least initially. The author could explain it better as the story progresses, potentially developing it in any way.
4- Same idea as the previous point: James wears a pendant with a Christian cross, and if I remember correctly, they exist in that world as well, and with the same meaning. It's too much of a coincidence for James to have at least made a comment about it, even if only a line, and I hope the author develops this further in the future, as religion seems to be a very important element in the plot.
Finally, I would like to thank the author, Kur, for giving us the opportunity to read this entertaining story. I know that writing a story involves a lot of effort, and even more so when presenting it as a visual novel. I eagerly await the next update and apologize if I've made any mistakes or haven't been very polite; I just wanted to give my honest opinion.