Sacrifice

Sacrifice (ソウルリリース) is a technique that was introduced in Kingdom Hearts Birth by Sleep. It allows the user to execute a powerful attack at the expense of HP, meaning that it can also be used to empower low-HP abilities like EXP Chance and Reload Boost. If used immediately before Limit Storm, the latter attack sports a red glow instead of a blue one, and executes much faster than normal.

Mechanics
In Kingdom Hearts Birth by Sleep, Sacrifice is an Ultimate attack command exclusive to Terra that takes one slot in the Command Deck, has a maximum level of 5, a normal reload time of 20 seconds, and fills the Command Gauge by 40%.

In Kingdom Hearts 3D: Dream Drop Distance, Sacrifice is an attack command exclusive to Riku that uses one slot in the Deck Command, and has a reload time of 26 seconds.

Kingdom Hearts Birth by Sleep

 * Terra can create Sacrifice through Command Melding.
 * Terra can purchase Sacrifice from a bonus panel on the Honeypot Board.
 * Terra can purchase Sacrifice from the Moogle Shop for 1500 munny once the command has already been obtained elsewhere.

Kingdom Hearts 3D: Dream Drop Distance

 * Sora and Riku can purchase Sacrifice from the Aura Lion Ability Link for 200 Link Points.
 * Sora and Riku can purchase Sacrifice from the Medal Shop for 1000 Medals.

Kingdom Hearts Birth by Sleep
Sacrifice is an Ultimate-class Attack Command that can be melded through two different recipes, listed in the Giga Attack Recipe.
 * The first recipe can only be melded by Terra, and is a recipe.
 * Dark Haze (LV4) + Warp (LV5)
 * The second recipe can only be melded by Terra, and is a recipe.
 * Warp (LV5) + Poison Edge (LV3)

Origin
Sacrifice is similar to the Souleater command in the Final Fantasy series, which usually allows the user to expend some of their HP to execute a strong attack.