Digimon: Zeo

Digimon Digital Monsters  (デジモンアドベンチャー, Dejimon Adobenchā ?) is a Japanese animated television series created by Akiyoshi Hongo and produced by Toei Animation based on the Digimon virtual pet made by Bandai and is the first anime installment in the Digimon media franchise. The series is continued with the same characters in Digimon Adventure 02.

The planning for Digimon Adventure started in 1998 and was done in cooperation by Toei Animation, Bandai and Fuji Television.

Plot
Upon returning, the Dark Masters, four elite evil Digimon, reveal themselves to be the true culprits behind every enemy the DigiDestined had faced thus far. As the DigiDestined battle them while losing allies in the process, they experience hardships of their own, including their group temporarily disbanding. However, all of them realize they cannot save the Digital World without each other, and once the last Dark Master is defeated, Apocalymon reveals himself to be their final enemy. Once he is defeated, the children returned to the Real World, leaving their Digimon partners behind