The Keyblade is a recurring weapon and often the main source of power for the protagonist in the Kingdom Hearts series. In Kingdom Hearts: Sinister, the Keyblade takes a major step away from what has been previously canon and features several original and off-beat variations.
Although the Keybaldes in Sinister do variate from the norm, they still retain many of the same abilities as before. Keyblades can open or close any lock, seal metaphysical things such as memories away, or unlock and release things such as hearts. They are also the only weapon, with certain special exceptions, capable of killing supernatural creatures such as the Heartless. In addition, they can empower any ally fighting along side the user with the ability to kill Heartless with a weapon of their choice. Finally, Keyblades wielded in Kingdom Hearts: Sinister can also change their appearance and ability based on the Keychain attached to them. (In Kingdom Hearts: Sinister, this feature is relegated under the Arms category)
A new tool in a Keyblader's arsenal is added in KHS, with the addition of the Release ability. Similar to Drive Forms, Command Styles, and Limit Breaks, the Release Gauge in Sinister is filled evey time a character recieves damage, strikes an enemy, or uses a magic or ability unique to them. Once filled, the gauage allows the use of a Keyblade's Release Form, similar to a Bankai in Bleach. The Release state only lasts for a certain period of time, depending on the size of the Gauge, which slowly drains after Release has been started. However, the player can opt to revert at any time. Once the Release Gauge is filled, a command appears in the player's Command Deck that allows an entry into Release Form, and then allows reversion. After a Revert or the Gauge is empty, the command dissapears.
While is Release Form, the character's attack strength, magical ability, and movement speed are increased, and the use of special abilities is allowed, similar to the Finish attack in Birth By Sleep.
Another new feature in Kingdom Hearts: Sinister is the Keyblade Fusion ability, which acts similar to the "Command Meld" in Birth By Sleep.