The Red Chain (Japanese: あかいくさり Red Chain) is an unobtainable key item
in Pokémon Diamond, Pearl, and Platinum, created from crystals drawn
from the Sinnoh's lake guardians. It is used by Cyrus to take control
over the legendary Pokémon Dialga and Palkia so as not to reduce their
power by capturing them in a Poké Ball, with the ultimate goal being
to destroy the universe and make a new one without spirit.
It is unknown what has happened to Cyrus in the game but in the anime he goes to the world he created.