The movie is mainly about Tai and Kari while they were little. Koromon mysteriously arrives in Highton View Terrace (where Tai and Kari live). About the same time, their city is attacked by a large, green bird digimon (later known as Parrotmon. The attack is later thought to be a terrorist bombing.) Somehow, Koromon digivolves into Greymon and saves Tai, Kari and the rest of the city.