Digimon 02 (Season 2)
Three (Earth) years after the events of Digimon Adventure, there's a new threat to the Digital World: the evil Digimon Emperor and his Dark Rings (like Black Gears). T.K. and Kari, both 11, are brought back to the Digital World, together with the new Digidestined: Yolei Inoue, Cody Hida, and Davis Motomiya.
The crests and tags are no longer used; instead, the kids find Armour-Eggs that let their Digimon armour-digivolve. The Digimon Emperor has stopped normal Digivolution with his control spires; however, armour-digivolution remains unaffected.
The Digimon Emperor is a Digidestined (genius Ken Ichijouji), and has the power to force Digimon that have Dark Rings to Dark-Digivolve, using his black D3 Digivice. Agumon (Tai's partner from Adventure) is forced to Dark-Digivolve to SkullGreymon.
Davis plays soccer against Ken, and gives him a bruise on the leg (accidentally). Later, in the Digital World, the kids find out that Ken is the Digimon Emperor.
Ken creates Kimeramon, an Ultimate level Digimon with parts from all kinds of other Digimon. T.K. goes off by himself (with Patamon) to find Ken and fight him. The kids infiltrate the Emperor's base and Davis finds his last Armour-Egg, a Golden one, powering the base. Veemon digivolves to Magnamon, but he can't defeat Kimeramon. Then, suddenly, Wormmon (Ken's partner) appears from the shadows to help Magnamon! Ken finally finds his true self and turns good again.
Cody is attacked by Thundermon while getting mad about all the damage inflicted on the Digital World by Ken, as the Digimon Emperor. A green Digimon appears and deletes Thundermon. It's later revealed that this Digimon is Wormmon, digivolved into Stingmon. Davis wants Ken to join the Digidestined team, but Ken always refuses, wanting to undo all his damage on his own.
A mysterious woman, Arukenimon, appears and starts turning control spires into evil Digimon. She wants to destroy the Digidestined, and when her trap fails she creates BlackWarGreymon to destroy the Destiny Stones that hold the Digital World together.
Control spires and Digimon start appearing all over Earth, and the Digidestined travel the world to destroy the spires. They meet a heap of other Digidestined and their Digimon. Meanwhile, a man named Oikawa has fallen to the Dark Side and tries to destroy all the Digidestined. The kids and Digimon help Oikawa see what's really in his heart, and his Digimon partner from when he was a kid returns! Davis shows all the kids whose hearts are filled with despair how to live their dreams, and everyone gets a Digimon. The Digital World is no longer a secret and everyone now has a Digimon partner.