Luke could react with a newfound sense of responsibility. Seeing Vader's fall, he might feel that it is his duty to help any other fallen Jedi or those who are on the brink of falling to the dark side. He might also have a moment of self - reflection, wondering if he could ever be tempted by the dark side in the same way Vader was.
In certain fanfictions, Luke sees Darth Vader's fall symbolically. For example, he might see the destruction that Vader has caused on a planet or to a group of people. This destruction represents Vader's fall from grace. It could be that Vader has ordered the massacre of innocents, and Luke witnesses the aftermath. This makes Luke realize the true nature of the dark side that Vader has embraced and how far he has fallen from being a Jedi.
One theme could be redemption. Seeing Vader's fall can symbolize his redemption from the dark side, and Luke witnessing it can be about the power of forgiveness and the possibility of change in the Star Wars universe.
A good fanfic about Luke and Darth Vader should first and foremost have a strong understanding of the characters. They need to stay true to their personalities as seen in the movies. For example, Vader's internal struggle between the light and dark side should be well - represented. Also, a great plot that ties into the existing Star Wars mythology is important. Maybe it could involve a new threat that forces Luke and Vader to work together, or explore their relationship in a different time period.
There's a fanfic titled 'Vader's Redemption'. In this story, Vader starts to question his loyalty to the Emperor much sooner, especially after some profound encounters with Luke. It's a great read as it shows the internal struggle of Vader while also exploring the bond between father and son in a new light. It's full of action-packed scenes and deep emotional moments.
His view could become more complex. Before, Vader was mainly an enemy. But seeing his fall, Luke might start to see him more as a tragic figure, a victim of the dark side's power.
Luke might be initially shocked. He has always seen Vader as this powerful and menacing figure. So, seeing him fall could bring a sense of disbelief. It could also stir mixed emotions in Luke, like a strange form of pity despite all the bad things Vader has done.
One popular fanfic could be 'The Redemption of Vader' where Luke witnesses Vader's fall in a very emotional and detailed way. It really delves into Luke's thoughts and feelings during that moment.
In some fanfiction, if Luke and Darth Vader teamed up, they could be an unstoppable force for good. They could use their combined Force abilities to fight against a greater evil in the galaxy. Maybe they would start by taking on the Emperor together, using Vader's knowledge of the Sith and Luke's purity in the Force.
Ezra's reaction would also depend on his state of mind at the time. If he was feeling confident and strong in the Force, he might be more bold in his approach to Vader. He could try to engage in a battle of wills through the Force, trying to push back against Vader's dark side influence. But if he was already weakened or doubting himself, the sight of Vader could make him feel hopeless and desperate, leading to a more erratic or panicked reaction.
There might be a fanfiction where Luke tries to redeem Darth Vader in a different way than in the original movies. Maybe he uses ancient Jedi teachings that were long forgotten to reach out to the good still left in Vader. This could lead to a whole new adventure and a different path for their relationship.