Second Form is a Formchange in Kingdom Hearts III. It grants Sora clothing based on his outfit from Kingdom Hearts II and gives him access to familiar abilities. It is triggered by the Kingdom Key, Starlight, Midnight Blue, Phantom Green, and Dawn Till Dusk. The Keyblade used determines the third level finisher.
Second Form changes Sora's clothes into the same colors and style of the clothes he wore in Kingdom Hearts II. While wearing his original outfit during the Olympus episode, Sora's clothes do not change.