.nuxt Directory
Nuxt uses the .nuxt/ directory in development to generate your Vue application.
You should not touch any files inside since the whole directory will be re-created when running nuxt dev.
This directory is interesting if you want to learn more about the files Nuxt generates based on your directory structure.
Virtual File System
Nuxt also provides a Virtual File System (VFS) for modules to add templates to this directory without writing them to disk. You can explore the generated files by navigating to http://localhost:3000/_vfs