Damage Control

Crisis Half is an ability that only appears in Kingdom Hearts II: Final Mix and Kingdom Hearts 358/2 Days. In 358/2 Days, it can be activated through the abilities of Roxas's and Xion's Fate Rebellion+. In Kingdom Hearts II: Final Mix, it can be used through the abilities of Goofy's Save the King+ and Donald's Centurion+. Oddly, this ability can only be used through upgraded weapons, as shown by the "+" at the end of their names.

Crisis Half makes you take 1/2 damage when you’re in Critical HP (a lot better than Defender, but stacks with it anyway). You can get it early by defeating Absent Silhouette Zexion (the glowing orb that shows up in the room with a save point before Hades’ chamber after you beat Demyx in the Underworld).