Based on the title, the most obvious main character would be the 'yuusha' (hero) who has returned from the isekai. There may also be other characters in the modern world that the hero interacts with, like normal humans who are amazed by his power or antagonists who oppose him because of his new - found strength in the modern era.
Since I haven't read the novel, I can't say for sure. But it's likely that the main character is the hero who returns from the isekai world.
I'm not sure specifically as I haven't read it. But generally, in the context of 'isekai' (another world) type novels, it might be about a hero who returns from another world and becomes the strongest in the modern world.
I don't know the main characters as I haven't read it. It could be a young hero with a special power or destiny.
Since I don't know the exact novel, I can't say for sure. But usually, there would be the hero who comes from another world. There might also be characters who help or oppose the hero in the new world.
The title implies that the main character is the powerful onmyouji. However, in an isekai story, there are usually other important characters. There could be a sidekick or a mentor - like figure that helps the onmyouji in his journey. There may also be villains or rivals, perhaps other powerful beings in the isekai world who see the onmyouji as a threat or a competitor. And of course, there might be characters that the onmyouji befriends, such as local villagers or other travelers in this new world.
Since I don't know the details of this novel, I can't say for sure who the main characters are. But it's likely that there is a character with assassination skills as one of the main characters.
Without having read the 'tsuki ga michibiku isekai novel', we can only guess at the main characters. It could be a hero - type character who is drawn to the isekai world by the moon's call. There might be a mentor - like figure in the new world who helps the protagonist understand the rules and powers related to the moon. And perhaps there are antagonists who oppose the protagonist's goals which may be related to the moon - influenced aspects of the isekai world.
As we only have the title'mondaiji tachi ga isekai novel', it's difficult to determine the main characters precisely. 'Mondaiji tachi' seems to be a likely candidate, but in isekai novels, sometimes the main character is someone who stands out among a group. There could be a leader - like figure within'mondaiji tachi' or perhaps a character with a special ability that drives the story forward. And of course, there could be other characters introduced later in the story that become just as important.
I'm not familiar with the specific details of this novel, but typically in such a story, the yandere kanojo would be a main character. There could be a male lead that she becomes obsessed with in the isekai world. And then there might be side characters like the local inhabitants of the isekai world, perhaps a wizard who helps or hinders her, or a group of warriors that she has to interact with depending on the plot of the novel.
I'm sorry I don't know the main characters as I haven't read the light novel. You could try looking for summaries or reviews online to find out.
Since I don't know the specific details of this light novel, I can't say for sure who the main characters are. But it could be some students from the class that was summoned.