Dyad in the Force

"The life force of your bond... a dyad in the Force. A power like life itself. Unseen for generations."

- Darth Sidious, to Rey Palpatine and Ben Solo

A Force dyad was a phenomenon, similar to a Force bond, describing two Force-sensitive beings who collectively shared the power of one individual, connecting them across space and time.

Description
When two beings were a dyad in the Force, their minds were bridged, allowing them to see each other across vast distances of space. When this occurred between Rey and Kylo Ren, they were able to see each other, but not where each other was. As their bond grew stronger, they were able to transfer part of their surroundings into the other's locations. For instance, a drop of rain. Later, they became capable of engaging in a lightsaber duel despite being in two different places. They could also hand off objects to each other through the Force.

In addition to objects, information could be shared across a dyad's bond. For instance, Rey was able to absorb Ren's knowledge of certain Force techniques during his attempt to probe her mind. This allowed his training to become hers and gave her some of his abilities, such as the ability to affect the minds of others with the Force. However, the downside to obtaining information this way was that it was a two way street, and Ren could often use their connection to project images into her head and even speak with her when he desired.

Another drawback was that certain malicious beings could use the bond against its users. For instance, Supreme Leader Snoke was able to encourage the mental link between Ren and Rey to tempt Rey into coming to him aboard the Supremacy. Darth Sidious, upon his revival, was also able to drain the powerful energy generated by the dyad to restore his withered and damaged body to a life-like state.

Finally, members of a dyad were able to share life energy through their bond. As a result, newly redeemed Ben Solo was capable of reviving Rey from the dead by transferring his life energy into her in order to resuscitate her.

History
Records of a Force dyad exist in the form of an incantation written out in the Sith old tongue by the Sith Eternal cultists, denoting the specific nature of the phenomenon. The text is near-identical to the Sith doctrine, the Rule of Two, but inflection marks and line breaks change specific meanings in certain words.

New Republic era
Rey Skywalker and Ben Solo, who shared a Force-bond, formed a Force dyad during the New Republic Era, during which time it had been the first seen in generations. As Kylo Ren, Ben revealed to Rey that they were a dyad in the Force during her mission to Kijimi with Finn and Poe Dameron in 35 ABY. Their Force dyad helped them not only to strengthen their physical bond, but their mental and emotional bond to the point that Darth Sidious even comments on how close they are within the Force.

When Rey and Ben came together to fight Darth Sidious during the battle at Exegol, the Sith Lord grabbed the two using the Force and inadvertently drew some of their life force, learning that they were a dyad in the process, despite Ben's attempts to hide it from him. Sidious then proceeded to exploit this by siphoning their powerful connection, rejuvenating himself while weakening the pair.

Appearances

 * Star Wars Episode VII The Force Awakens
 * Star Wars: Episode VIII The Last Jedi
 * Star Wars: Episode IX The Rise of Skywalker
 * Star Wars: The Last Jedi: Expanded Edition