Star Wars: 10 Most Powerful Things Darth Vader Ever Did
10. Rejected A Vision Where He Returned To The Light Side - Darth Vader #5
Although Darth Vader would eventually redeem himself at the end of Return of the Jedi (1983), this only occurred after more than twenty years of suppressing what was left of Anakin Skywalker. One early instance of this happened right after Vader had battled surviving Jedi Kirak Infil'a for his lightsaber (more on that later).
Once he had claimed the weapon, Vader was told to go to Mustafar in order to make the kyber crystal inside "bleed", i.e. pouring all of his rage and hatred into it so that it would be corrupted and produce a red blade. As Vader went about doing this, the energy inside the crystal forced him to hallucinate a different series of events in order to dissuade him from carrying the bleeding out (the kyber crystal was a sentient being, of course).
Within the vision, Vader turned his back on the dark side by travelling to Coruscant and killing Emperor Palpatine. Once that was done, he found Obi-Wan Kenobi and begged for forgiveness for the atrocities he had committed. Everything seemed to be going well for a moment, until Obi-Wan referred to him as "Anakin", which enraged Vader enough to dismiss the hallucinations entirely and complete the bleeding process.
This would be Vader's first rejection of the good left within him, but it would certainly not be his last. For the time being, Darth Vader was consumed by the dark side of the Force.
But at least he got a shiny new red lightsaber out of it, so that's a plus.