The Unity Badge (共闘の証, Kyoutou no Akashi?, lit. "Unity Proof") is a special reward found in Kingdom Hearts 358/2 Days that allows a player to open a particular Mission in Mission Mode. Beginning in Mission 16, they must be found in the world in order for that Mission to open. A Unity Badge will show in a world as a small red badge with a silver ridge and decor.
Some earlier Missions can be played in Mission Mode, but a Unity Badge is not required to open them; they are considered open once the player completes the mission.
Unity Badge Locations