Reincarnated as a Slime

Isekai can be tricky even though it looks easy.  People think it’s only about having someone transported to another world and leave it at that.  Makes sense since this means the main character acts as an avatar for the audience.  Still, there are plenty of ways to screw this up, especially now that the subgenre is oversaturated.  What can you do to avoid the common pitfalls?

1. You really need to show what the main character was like in their old life.  It doesn’t have to be immediately or at once.  This can be information that is doled out in pieces when the character has a memory or concept triggered.  Ignoring their previous life eliminates an essential dimension and weakens the fact that they are a stranger in an alien world.  It doesn’t really feel like they’ve been removed from an old life anymore because the reader has no knowledge of it.
2. The greatest danger is the overpowered main character.  Typically, the transported person has greater abilities and knowledge than the locals.  They’re not so much a chosen one, but are special.  With fantasy, this tends to come out as incredible magic and powers that dwarf everyone else.  They become Superman on steroids because authors don’t always remember to add a weakness.  You need to introduce a feasible threat at some point.  If they’re wrecking all adversaries for the entire story then it’s an empty power fantasy.  For example, Rimiru in ‘Reincarnated as a Slime’ was defeating everyone with increasing ease.  Then, he ran into an anime that nearly killed him because they negated his strengths.  This revived the tension and changed him from an unstoppable protagonist to one who needs to grow.
3. Being transported to a different world doesn’t mean the main character changes their personality.  They may do this over time, but they don’t appear and then immediately become someone new.  Part of the story is that they are their old selves and need to grow into a new version to survive.  Some will see it as a clean slate and try to be someone new at the start.  This makes sense, but it shouldn’t be a perfect change and the older habits need to be maintained for some time.  Otherwise, what’s the point of writing an isekai when you can do the same with a confused protagonist from that same world?
4. Not every transported character needs to be catnip to the locals.  They may be curiosities if their origins are known.  It gets ridiculous when every named character ends up wanting to marry, kiss, hug, or bed the hero.  This happens a lot with absolutely no explanation other than ‘this guy/girl is now cool’.
5. Even if the hero knows about the world before being transported, you should surprise them.  They might not know the exact physics of the world or the cultures even if it’s based on media in their world.  Think about how we’re told to write a story using only the exciting parts of our characters’ lives.  If we were dropped into any of these worlds, we wouldn’t know about anything that was deemed unimportant.  Daily life events, holidays that did not happen in the story, unessential historical events, and cultural traditions are only some of what can be thrown at the hero.
6. If the character’s cellphone is going to still work in this other world, please explain how it still has a signal and doesn’t run out of battery power.  I know this one is specific, but I’ve noticed at least two Isekai that involve smartphones.  I only watched one of them, which I didn’t like.  It was the main one either.  Still, I couldn’t figure out how the character was in this medieval setting for two years and his phone still had power and a signal.  In fact, explain how any modern technology continues to work for an extended period of time.
7. You don’t have to decide at the beginning if the character wants to go back home or not.  Of course, this doesn’t matter if they died and woke up in the new world, which implies that they’re stuck.  If that’s not the case then you can play with both possibilities.  Any person who wakes up in a new world may want to explore, especially if it’s one they recognize from various media.  The desire to go back home may need to be triggered by a sense of that this isn’t a game or fiction.  So, focus on world and character building instead of the finale for a bit.  You can always change from one to the other as well.