It's a re-telling of the story of how the original 8 digidestined became
the digidestined. It's the story that was told in episode 45 (The Ultimate
Clash). One night, when they all lived at Highton View Terrance, a Koromon
came from the digiworld and digivolved to Greymon. They saw the fight
between Greymon and Parrotmon. They 8 children who saw the battle grew up
to be the digidestined. During the battle a light processed their
information leading too the creation of the tags, crests, and digivices.
This is also when these devices were linked to the digimon and children.