Writing Tips and Reviews

Characters stating common knowledge

If a character is a resident of the world, they should not state what is common knowledge to them. Think about this way, you play Pokémon, do you need to tell everyone who also plays what a pokeball is? No? Exactly.

Speaking of demons, Welcome to Demon School is a good example. The protagonist is a human who is brought into the demon world, meaning he doesn't know anything. This gives the writers an excuse to explain the world. If Iruma was a demon who was born into the world and we followed him growing up, that would also be an excuse to explain the world. If we, for example, followed Alice, we would not get any explanation. Why would he need to? Anything he knows is common knowledge. We wouldn't see a line such as, "it was obvious he wasn't human," in the light novel because... NO DUH.

A land of demons does not point out how everyone is demons and treat that as weird. Not without someone from the outside. The demons in Welcome to Demon school never say how strange it is that they're demons, they point out weird people, but see it as we do with strangers in our world. When talking about books about the torture or monsters, Alice treats it the same as we treat a book about biology. Only Iruma freaks out because he's not from the world.

How about My Next Life as a Villainess? Katarina knows about the world and explains it because she needs to know certain information to avoid death flags. We don't hear how weird or different the world is from the other characters as they do not know anything else. Keith was born and raised in this world, so sees everything as normal. Even Katarina's weird antics are normal. He points out how she's "doing it again," but never talks about who strange it is since he's used to it. He'll never say how strange it is she's acting that way or how weird it is noble's have magic, because that's how the world works. 

Rin Tohsaka from Fate Stay Night will never say how strange it is that mages can preform magic or that servants can be summoned to fight in a war. She has to explain it to Shirou, but she wouldn't explain it to Illia or Shinji. They're from mage families as well, they should know. Even Fujimaru doesn't need an explanation of how the world works or treats everyday occurrences as strange.

This is why writers like to use amnesia or isekai stories, as it gives  them an excuse to explain the world. Following a resident is much harder as they have to state the information in a different way. Sometimes the character is talking to the audience, they hear the basics through a teacher and are bored, or have to read a book. No matter what path the writer chooses, the character should only be surprised when it's new information. Alice being surprised he's a demon would only work if he had amnesia and was in the human realm. Otherwise it would be stupid on his end.