Warning: This book has a large harem, and it will be cringe. Don't expect good character development or writing.
This book wasn't made for that. It's just a Solo Leveling glaze plus Pokémon harem book.
It's a game I've wanted to read a fanfic about, but the lore is so scattered, I've given up hope that anyone would write a fanfic about it.
Because of this, I did what anyone would do: go back and reread the in-game lore and decide to write a fanfic about it, because why not?
And this is a case of: you can't write this book without a harem, because there's just no way with the amount of things going on in that game.
The MC is OP. He's not human; he's a reincarnated soul, but most of his memories have been overwritten. There's a good explanation for it. So just read it, and you'll understand.
Now, "massive" is a vague word, but trust me. I can't decide on around five or ten or that number, but I'll try to tone it down and pick the ones from the game I like.
My current choices are Niz, Yora, Levia Damonica, Daisy, and Lilith. The rest will be discussed later.
Naturally, the name of the game is Echocalypse, and a search would reveal that.
While I can't say the writing is good, I enjoy playing the game and its lore. I believe that if you enjoy it, the quality of the writing is irrelevant.
Good writing or character development is not my aim here.
Turn off your brain, read it. There will be lots of terms you might not understand, but it'll be explained.