Name of the novel: Metalfield
Brief Summary: The peaceful Earth was suddenly invaded by unknown creatures. There was no salvation; human weapons doesn't work on them. Electricity died, society regressed-- the world completely changed. A twin, living in the middle of the woods, detached from the world, encounters these creatures. Watch as they uncover the mysteries hidden in this invasion. (tags: Action, Adventure, Fantasy, Sword and Magic, and a little Comedy)
Link to the novel: https://www.webnovel.com/book/12732365206947305/Metalfield