Taichi and the others were shaken by the death of Leomon, and Koushiro proposed to find out the truth about Mainemon's infection. But Meiko, the owner of Mainemon, couldn't think of why Mainemon was infected. In order to prevent other Digimon from being infected, Koushiro set up an isolation area in the office, but Patamon had already shown signs of being infected... At this time, the Digimon told everyone a big secret about the Digimon world. Faced with the truth of the secret and the reappearance of Mainemon, Taichi and the others fell into distress, and in the collision of their own ideas, they also made their own decisions... "If you always think about what will happen one day, you will become an adult unknowingly." Now, adventure evolves again.