I've been mulling over writing a story that would be and Isekai with some litRpg elements. But as these are both new genres for me, I'm curious as to what are the requirements to belong in those genres? How much 'system' does a litRpg need to show to qualify? Do you have to have a working set of game mechanics, or just levels and numbers? Does it have to be fantasy (I was thinking of superheroes actually) for Isekai?
I've read a few litrpgs and isekai, but I'm not totally immersed in those genres. I am trying to pick up some more though.
LitRPG is short for Literary RPG. What this means is, you write a story as if you're playing an RPG game. What system you want is entirely up to you. Maybe you want to make the standard Diablo-clone type of story, which means your story would have 'Strength, Agility, Constitution, Intelligence, Magic List and Current Buffs'. If you want to make something like DnD instead, you would probably add Perks and Feats as well. Maybe you'd have Level too.
Or you could make it low litrpg and just give them classes and learned skills but otherwise not allow them to rise in level, only proficiencies. That can work too. Basically, if it works as an RPG game, it is litrpg.
Isekai is simply 'another world'. Yes, that's the exact meaning. It's not superhero genre. For an isekai to be isekai, there must be another world being a consistent plot in the story. If your character was supposed to go to another world, but didn't due to some reason, that's not isekai. However, if his entire class goes to another world and we get scenes of them surviving in another world, then that is isekai.
Isekai doesn't have to be fantasy. It can also be sci-fi. If your character ends up in another planet or alternate reality due to some strange quantum anomaly, that's also isekai. The difference is, it's a sci-fi isekai with no magic. Maybe instead of getting magic powers, your protagonist steals a plasma pulse rifle and continues to slaughter ugly alien scum because he's a human supremacist in a world without humans.
Stephen King's The Dark Tower and its universe can also be considered isekai. The 10th Kingdom, a Hallmark movie is also isekai.
Isekai and litrpg are two completely different things. They can work together, but they don't have to work together. You can make isekai without magic. Even if you make the protagonist a normal person in another world, that's still isekai.