An unexpected trip by an alien brings the protagonist back to the past. As a reward, the protagonist is given a cheating device.
Live a low-key life, develop in a low-key manner, dig holes, farm, mine, steel-making, guns, cannons, aircraft missiles and submarine torpedoes, and fight World War II with 21st century weapons.
If you want to kill people, kill them to your heart's content, and if you destroy the sun, kill them all, but before that, you should keep a low profile and keep your tail between your legs.
Cool article! ! ! !