Four of the DigiKeys in the holy altar.
The DigiKeys (鍵 Kagi?, lit. "Key") are items in Digimon Get Back. They have the power of the Ten Legendary Warriors and are unlocked by each DigiDestined. Each one is emblazoned with a Crest.
The DigiDestined were supposed to place the five keys in a holy altar in order to clear the Dark King's fog, but because Taro Osanai refused to becme a DigiDestined, they were missing one DigiKey and were defeated. When Osanai finally unlocks the DigiKey of Courage, they are able to save the Digital World.
List of Keys
DigiKey of Courage

The DigiKey of Courage (勇気の鍵 Yuuki no Kagi?, lit. "Key of Courage") is embodied by Taro Osanai. It is engraved with the Crest of Courage.
The DigiDestined learned from AncientGreymon that none of them could make the final DigiKey, because it requires not a fearless heart, but a fearful heart willing to take the first steps to overcome fear. When Taro Osanai finally accepts to become a DigiDestined, the DigiKey of Courage emerges from his Digivice. When Agumon defends Osanai from SkullSatamon, the man feels power welling up in the DigiKey, and Agumon warp digivolves to Dinomon.
When Osanai starts to disappear after SkullSatamon's defeat because of a time paradox, he gives the DigiKey to Akira Matsukita so the DigiDestined can gather all five DigiKeys and eventually return home.
DigiKey of Friendship

The DigiKey of Friendship (友情の鍵 Yuujou no Kagi?, lit. "Key of Friendship") is embodied by Akira Matsukita. It is engraved with the Crest of Friendship.
Akira shows Taro Osanai the DigiKey when explaining the DigiDestined's past battles and defeat.