Tell me the name of the film

I watched this movie with my family at home a long time ago, please tell me that I didn’t imagine it… The movie was possibly Japanese, most likely Korean. I don’t know the exact details of the story, but in the movie there was an author of a book and everything he wrote there appeared in the real world or it was in a separate world but somehow influenced our world. The author of the book of course doesn’t know this, but the main character somehow finds out that this book influences our world and it seems like everything there almost reaches the end of the world, but the main character gets into the world of the book and at the end fights a boss, he was huge, but he looked like a human. The special effects were pretty impressive. That’s all I remember. I wouldn’t be surprised if no one knows the name, but I really want to watch this movie again.

Death Note?