Valerian and Laureline by... - Where Stories Are Born

The Delphs are an artificial species who depend entirely on an
extremely rare substance, that not only allows them to live and
reproduce, but also fuels their creative talents – for the Delphs are
the most sought-after storytellers in the galaxy. They call upon
Galaxity to find a new source of it, as their own is exhausted. The
problem is, the only available deposit is on 21st century Earth, and
the agents on station … are still going to high school!