The Great Leader of the Second Imperium was a holographic facsimile of the deceased Dark Lord of the Sith and Galactic Emperor Palpatine, created by four unidentified Imperial Royal Guards to serve as figure head for their fledgling empire.
The four Royal Guards founded the Second Imperium and by impersonating Palpatine, the deceased Sith Lord Darth Sidious, using holograms stretching from his earliest days as the Senator of Naboo to Supreme Chancellor of the Galactic Republic and finally to Emperor of the Empire drew many into their fold.
Following a series of raids on the New Republic the four Royal Guards arrived at the Shadow Academy with Palpatine supposedly residing in a massive repulsorlift isolation chamber. The Royal Guards prevented Brakiss from visiting the Emperor, causing him to be concerned about the Emperor's health. Later, from his isolation chamber, "Palpatine" prompted Brakiss to launch an assault against the Jedi Praxeum on Yavin 4.
At first the battle played out as planned. A Second Imperium ground force consisting of Stormtroopers and Dark Jedi surrounded the Jedi Praxeum while TIE fighters and TIE/sa Bombers bombed the surrounding jungle. In space, the Shadow Academy and a fleet of refitted Star Destroyers and battle cruisers blockaded Yavin 4. This changed with the arrival of the New Republic fleet under Admiral Gial Ackbar and Brakiss' defeat during a single combat with his former Master. Having made it back to the space station, Brakiss made his way to the isolation chamber and demanded to see the Emperor. However, he was blocked by two of the Royal Guards. Enraged and giving in to his anger, Brakiss cut them down with his lightsaber and then entered the chamber.
There, he discovered a third Royal Guard working on a bank of controls, computer screens and holographic generators and realized that the Emperor had never returned. In reality, the Royal Guards had created the illusionary Darth Sidious so that they could control the Second Imperium. Unfortunately for Brakiss, the fourth guard used his "Emperor's" override controls to activate the Shadow Academy's self-destruct systems, destroying the Academy and killing all onboard. With the destruction of the Shadow Academy, the battle turned in favor of the New Republic and the remaining Imperium troops and Dark Jedi were presumably captured by the New Republic and the Imperial Remnant.
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