After the Clone Wars and Order 66,Darth Vader always knew his former apprentice Ahsoka Tano was alive and that he would one day face her in battle — long before it happened in Star Wars Rebels. Ahsoka Tano unwittingly played a crucial role in Anakin Skywalker's fall to the dark side. When she left the Jedi, she shook his confidence in the Jedi Council. Tragically, during the Siege of Mandalore she was given information that could have saved Anakin — had she been given the opportunity to pass it on. The bond between master and apprentice remained strong, though, and she sensed his fall to the dark side. As seen in Star Wars: The Clone Wars season 7, this left her shaken — and possibly helped her survive Order 66.
Ahsoka wouldn't cross paths with her master again until Star Wars Rebels, when she came face to face with Darth Vader on the Sith planet Malachor. She would have died had Ezra Bridger not intervened from the World Between Worlds, plucking her out of the collapsing Sith temple before she was crushed. Surprisingly, though, this duel was not a surprise to Darth Vader himself. He had always known he would eventually fight Ahsoka Tano.
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The 2017 comicDarth Vader #25 by Charles Soule and Giuseppe Camuncoli is set shortly after the events of Star Wars: Episode III — Revenge of the Sith. It sees Darth Vader use the power of a Force vergence on Mustafar to tear open space and time in an attempt to resurrect his beloved Padmé. He enters into a realm akin to the World Between Worlds, where he experiences visions of the past and the future, some of which are symbolic representations rather than "real" history. Some of these visions center on Ahsoka, and
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