Dimension Link

The Dimension Link (ディメンションリンク), also known as D-Link, is a feature of summoning in Kingdom Hearts Birth by Sleep. It's name connects to its purpose as a link to summon a character's power from another world. The power originates from a spell Aqua puts on the Wayfinders she and her friends carry. The characters create D-Links with those they form friendships with throughout their adventure or if they are controlled by a character (Maleficent and Terra).

Usage
To use the D-Link (or Dimension Link) system, it must be added as a D-Link Command in its own separate D-Link menu and can only be used when the D-Link gauge is full. The D-Link gauge is blue and next to the HP meter. The D-link gauge is filled by obtaining dropped blue diamond-shaped prizes from enemies similar to obtaining Drive Orbs to fill the Drive Gauge in Kingdom Hearts II.

Once the characters have been linked, the Command gauge changes to indicate the linked character, including his or her name, and the face of the linked companion will show up on the bottom right of the screen. When initiating a D-Link, a character's HP will immediately be fully replenished. By linking to a character, the character using the link will be able to use a set of commands and a unique Finisher. During a D-Link, any defeated enemy will have a chance of dropping an emblem, and collecting it will raise the D-Link's level, adding an ability (represented by the symbols to the left to the linked companion's face) and more commands. Up to two emblems can be collected for each D-Link, and after the second emblem the user will have access to a different, more powerful Finisher. Any emblems collected while using a D-Link that's already at Level 2 will simply refill the D-Link gauge. While linked, the D-Link gauge decreases continuously, and the link is broken when the gauge is completely empty, or when the player moves to another map or brings up the main menu.

The player is also able to D-Link their friends while using their wireless functions. They appear as Terra, Aqua or Ventus in their armor (including the corresponding D-Link abilities), as Deck Commands and Finish Command will be set as the ones the player's friend will be using when the D-Link is activated, granting the use of other characters' exclusive Deck and Finish Commands (such as Air Flair, Rising Rock, Magic Pulse or Meteor) with all characters, using wireless D-Link.

D-Links can be disabled for in-battle use in order to shorten the D-Link menu, notably when a player has many friends as D-Links.