You are an ordinary person, unremarkable your entire life. But before you die, you decide to go wild.
You purchase every service offered for your funeral, planning to play a little joke on your family before you die.
You have to admit, they did a pretty good job. Not only your family, but everyone starts believing that you used to be a Kamen Rider, an Ultraman, a special forces soldier, or something else entirely.
How do you know this?
Because hundreds of years later, when humanity faces an invasion by enemies from another world, all the newly developed magic, technology, occult arts, and body-tempering techniques prove useless. They revive you as humanity's ultimate weapon, a hero from history.
And your only skill is... a basic attack parry.
Theme: Don't joke around carelessly