Great replies, thanks. I'll be more specific. Maybe it will help the discussion and get me more specific input.
I am designing a skirmish game on YouTube, but having a break to work on the video quality. The game is roughly on the 90s cartoon the Visionaries, but with a little bit more realism.
Humans are living on a futuristic planet, but suddenly all technology stops. In the cartoon, the sun changes colour, magically stops technology from working and pours magic into the world. In my game I wanted it that technology was powered by a radiation emitted by the star/sun. This radiation stops and so does all technology.
Then the human survivors form new medieval like societies on a barren planet.
I have ideas on the societies but I am struggling to add back in the fantastical elements. Perhaps dormant aliens have awoken? Solar powered mining robots from before the super solar energy was discovered? Scientifically created monsters?