Countdown to Tokyo's Annihilation

Countdown to Tokyo's Annihilation (東京消滅 カウントダウン, Tōkyō Shōmetsu Kauntodaun) is the eighteenth episode of Digimon Adventure:

Summary
The Chosen Ones worked together and succeeded in defeating Ultimate Digimon Orochimon. However, a mysterious countdown begins. To save Tokyo, they must prevent it from reaching zero.