A Jedi and Sith holocron coming together
The merging of a Jedi holocron with a Sith holocron, known as holocron fusion, had the potential to unlock answers to any inquiry posed by those orchestrating the event. This process demanded collaboration between a practitioner of the dark side and a follower of the light side, each responsible for activating their respective holocron. Consequently, instances of such fusions were infrequent. Premature termination of the fusion risked the destruction of the involved holocrons, potentially leaving both Force users with fragmented insights into the other's sought-after knowledge. Furthermore, intense emotional states could distort the information yielded by the fusion. By the time the Galactic Civil War was approaching, the knowledge of holocron fusions had become scarce.
Holocron fusions were executed by simultaneously activating a Jedi and Sith holocron in the same location. This action caused the two holocrons to converge and meld together, granting those performing the ritual access to answers for any question they posed. The rarity of these fusions stemmed from the necessity for willing cooperation between users of the dark and light sides of the Force.
Interrupting a fusion before its natural conclusion could result in the destruction of the holocrons used, and the Force users involved would only receive fragments of the information that the other was trying to obtain. Moreover, strong emotions present during the fusion had the potential to warp the answers provided.
In the year 2 BBY, Maul, a former Sith Lord, captured the crew of the rebel starship Ghost, aware that Kanan Jarrus and Ezra Bridger, the Jedi members of the crew, possessed both a Jedi and a Sith holocron. Maul's previous encounter with the two Jedi informed his actions. He used reprogrammed tour guide droids to hold the other Spectres – Hera Syndulla, Sabine Wren, Garazeb Orrelios, and Chopper – hostage on the ship, compelling the Jedi to retrieve the Sith holocron, which Kanan had entrusted to a mysterious Force wielder known as the Bendu. Kanan's Jedi holocron was always stored within his cabin on the Ghost. After the retrieval of the Sith holocron, the Bendu enlightened Kanan and Ezra about holocron fusions, cautioning them about the potential for immense destruction. The two Jedi then met Maul at Vizsla Keep 09, where he was holding the Ghost. Following an attempt to kill Kanan and an order to his droids to execute the prisoners, Maul coerced Ezra, who had been immediately escorted to the station's control room, into initiating the fusion. Ezra sought "the key to destroying the Sith," while Maul professed to desire only "hope." However, Maul's true objective was to ascertain whether his nemesis, Obi-Wan Kenobi, was still alive, and if so, to discover his location for a confrontation.
As the fusion deepened, the other Spectres arrived at the control room. Kanan urged Ezra to avert his gaze, reminding him of the Bendu's warning. The Padawan eventually complied, abruptly ending the fusion and destroying the holocrons. Maul learned of Kenobi's survival, but Ezra was left with only fragmented visions of various locations, some familiar, others not.
Because the fusion was prematurely terminated, Maul and Ezra experienced a mixing of information between them. Maul gained knowledge of the location of Chopper Base on Atollon, the operational base for the Spectres and Phoenix Cell. He later tracked Ezra and Kanan to the planet and convinced Ezra to travel to Dathomir to participate in a ritual that would supposedly reveal the information they each sought. Through this, Maul discovered that Kenobi resided on Tatooine, while Ezra glimpsed that the Jedi Master held the key to the Sith's demise. Months afterward, Maul, failing to locate Kenobi in Tatooine's vast desert, used a fragment of the Sith holocron he had kept to lure Ezra to the planet. The plan succeeded, leading Ezra and Chopper to become lost and face near-death, which drew Kenobi out of hiding to assist them. When Ezra insisted that Kenobi was the key to destroying the Sith, based on the fusion's revelation, the Jedi Master clarified that Maul's desires had influenced the fusion, showing Ezra what the former Sith wanted to believe. Ezra and Chopper were then sent back to Atollon just before Maul arrived, and Kenobi defeated and killed the weakened darksider in a duel.
During the Imperial Era, the scholar Kian Derar uncovered a legend concerning the fusion, inscribed on the wall of a Jedi temple. The inscription described the fusion as a vergence. Inspired by this knowledge, Derar hoped to exploit the fusion to bypass Imperial intelligence.
The concept of a holocron fusion was introduced in the Star Wars Rebels season 3 episode "The Holocrons of Fate." The term "holocron fusion" was first officially used in the reference book Unlimited Power.