You must have a legal digital backup (.cia or .3ds file) of your Pokémon Sun game.
: Run the randomizer launcher on your PC (ensure you have Java installed) .
Alola's regional Pokédex is relatively small (302). An updated randomizer often pulls from the National Dex (807 in Ultra Sun/Moon) . This means:
Usually, when you black out, you wake up at the Pokémon Center or your house. Leo didn't wake up. The screen went black.