Proof

The Proofs are sets of key items which appear in Kingdom Hearts II Final Mix and Kingdom Hearts III, which are obtained after completing specific side-missions.

Kingdom Hearts II Final Mix
The Proof of Connection is obtained by defeating the Lingering Will, the Proof of Nonexistence is rewarded after defeating all of Organization XIII's Replica Data, and the Proof of Peace is given after appeasing the entire Mushroom XIII. Possessing a Proof grants Sora a crown costume modification.

Kingdom Hearts III
Added in update 1.04 on April 23, 2019, the Proof of Promises is obtained by photographing all 90 Lucky Emblems and clearing the game, while the Proof of Times Past is obtained by clearing the game in Critical Mode. Proofs carry over through New Game+.

As of version 1.07, released on January 22, 2020, the Proof of Promises and Proof of Times Past can be exchanged at the Moogle Shop for the Oathkeeper and Oblivion, respectively.

Design
In Kingdom Hearts II Final Mix, the Proofs appear as silver orbs with a dark symbol etched onto them. The Proof of Connection has a key symbol, the Proof of Nonexistence has the Nobody emblem, and the Proof of Peace has the head of a Mushroom.

In Kingdom Hearts III, the Proofs appear as a single piece of paper with two wings on the sides and an emblem on the top. There is a pattern adorned across the sides, and text can be seen written on the paper. The wings, emblem, and color scheme of the Proofs respectively resemble the guard, Keychain, and color scheme of the Keyblades they can be exchanged for; the Proof of Promises is themed after Oathkeeper, while the Proof of Times Past is themed after Oblivion.