The Siege of Lasan, also known as the Fall of Lasan, the cleansing of Lasan, or the Lasan genocide, was an Imperial invasion orchestrated by Alexsandr Kallus that saw the near-extinction of the Lasat species. During the early years of the Empire, the Imperial Military brutally suppressed an uprising on the Lasat homeworld of Lasan. The conflict led to the near-extinction of the Lasat people and caused the Imperial Senate to ban T-7 ion disruptor rifles. Some Lasat survived, like Garazeb Orrelios, who later joined the rebellion, while others like Gron and Chava resettled on the mystical Lasat refuge of Lira San.
The Lasat species originated on the remote planet of Lira San in Wild Space. At some unknown point, a large number of Lasat colonized the planet Lasan and eventually lost contact with their kind on Lira San. The Lasat on Lasan established a royal family and came to regard Lasan as their species' homeworld. Following the end of the Clone Wars, the Galactic Republic was transformed into the Galactic Empire. When the Lasat challenged the Empire, Imperial forces invaded their adopted homeworld, beginning the Siege of Lasan.
Following an uprising on the species' homeworld of Lasan, Agent Alexsandr Kallus of the Imperial Security Bureau was tasked with wiping out the rebellion in 7 BBY. Although it was not his idea to use the weapons, Imperial soldiers under Kallus used T-7 ion disruptor rifles against the Lasat civilians as a show of Imperial might. After defeating a member of the Lasan High Honor Guard, the guard then gave Kallus his J-19 bo-rifle in accordance with the Boosahn Keeraw, the Lasat warrior way. A number of Wookiee soldiers armed with weapons whittled from the wroshyr trees of their home planet also took part in the battle, sacrificing their own lives to try to prevent the massacres on Lasan. Thanks to the Wookiees' intervention, some Lasat were saved.
Among the Lasat who survived were Garazeb Orrelios, or referred to simply as "Zeb," a captain in the Lasan High Honor Guard, and his grandmother. During the battle, Orrelios was tasked with protecting the royal family and Lasat. However, he was knocked out by an explosion. When he awoke, Orrelios found that everything had been destroyed and blamed himself for failing to carry out his duty. Orrelios was haunted by his experiences during the Fall and harbored a deep hatred for the Empire. Those Lasat survivors who were captured by the Empire ended up in prison camps.
The Siege of Lasan ended with the devastation of the planet and the near-extinction of the Lasat species. As a result of the atrocity, the Imperial Senate banned the use of the T-7 disruptors and the rifles were recalled and destroyed. The atrocity's evidence was seen by Taris's senator Tynnra Pamlo. However, copies of the T-7 schematics escaped deletion and private weapons manufacturers continued to produce batches found on the black market. After what he saw as his failure on Lasan, Orrelios felt lost until he was found by the former Jedi Kanan Jarrus, who gave him new purpose as part of the Spectres crew, which evolved into a found family.
The Empire secretly planned to acquire some surviving T-7 stock to restart production of them on the planet Lothal, where the Spectres operated. The Imperial plan was disrupted by the Spectres and R2-D2, who destroyed half of the ion disruptors and sold the rest to the crime lord Cikatro Vizago. During the skirmish, Kallus personally fought Orrelios and taunted the Lasat about his role in the fall of Lasan.
Three years before the Battle of Yavin, the Spectres helped two other Lasat refugees, the former Honor Guard Gron and the mystic Chava, to rediscover the planet Lira San. During the journey, Gron contended that Lasan had not been destroyed but had been merely transformed in order to fulfill an ancient Lasat prophecy around Lira San. This prophecy held that Lira San could only be found if a "child of Lasan" saved the fool and the warrior from destruction. Following the rediscovery of Lira San, the rebels designated the planet as a sanctuary for other Lasat refugees.
Later, the fall of Lasan became a subject of conversation between Orrelios and Agent Kallus. The two adversaries had become stranded on the ice moon of Bahryn following an Imperial ambush above Geonosis. After Kallus recounted how he had obtained his bo-rifle from a fallen Lasat warrior, Kallus confided that he had not expected the Empire to unleash a massacre on Lasan and stressed that this was nothing personal. He also admitted that despite having taken credit for the use of the T-7 ion disruptor rifles, their use had not really been his idea. Orrelios reassured his adversary that he had made peace with the past already. As a gesture of reconciliation, he presented Kallus with a Bahryn meteorite as a parting gift.
Because of his time on Bahryn with Orrelios, Kallus defected to the rebellion, serving as a new Fulcrum agent. However, while Kallus was an undercover spy for sometime, he was discovered by Grand Admiral Thrawn and fully joined the rebellion after being rescued during the last stages of the Battle of Atollon. After the Galactic Civil War, Orrelios took Kallus through the secret hyperspace route to Lira San, where Kallus saw that he had not destroyed the Lasat people and was welcomed to join them.
Imperial defector Yrica Quell considered the difference between Alderaan's destruction, as well as genocides on Lasan and Dhen-Moh, and Operation: Cinder to be the difference between ruthlessness and cruelty.
The Siege of Lasan was first briefly alluded to in the television movie Star Wars Rebels: Spark of Rebellion, which first premiered on Disney XD on September 26, 2014. It was first mentioned in the first Star Wars Rebels episode "Droids in Distress," which premiered on October 3, 2014.