Well, usually the protagonist is a central character. In this web novel, it's likely to be the one who gets backstabbed in the backwater dungeon. They are probably on a journey of self - discovery and power - seeking within the dungeon.
I'm not sure specifically as I haven't read the light novel in full. But usually in such stories, there could be a brave adventurer who is initially trusting but gets betrayed. There might also be a cunning villain who does the backstabbing.
Well, one key feature might be its unique setting in a backwater dungeon which can offer a different kind of adventure compared to more common fantasy settings. It could also have complex characters who are likely to engage in backstabbing, adding lots of drama and plot twists.
One common plot twist could be the true identity of a seemingly friendly character being revealed as an enemy. For example, a character who has been helping the protagonist throughout their dungeon exploration turns out to be working for a rival group, secretly undermining the protagonist's progress.