In some cases, Vader could respond in a more subdued way. His voice might be tinged with a bit of sadness or regret. He may remember the time before he turned to the dark side and how things used to be with Luke. So instead of an immediate aggressive reaction, he might ask Luke why he is calling out to him in a rather weary tone, as if he is tired of all the conflict between them.
He may respond with anger at first. Vader has been so entrenched in the dark side that Luke's call could be seen as a threat to his new identity. But then, as he contemplates it more, there could be a hint of curiosity. He might wonder what Luke wants from him, especially if he still has some lingering feelings for his son deep down. For example, in some fanfictions, he growls out a demand for Luke to state his purpose, but his tone might not be as menacing as it usually is when facing an enemy.
Vader might initially be shocked. His son reaching out to him is unexpected. He could respond with a moment of silence, trying to process what is happening.
This would be a huge twist. It might mean Luke is seduced by the dark side's power or has some ulterior motive for joining Vader. It could change the course of the entire story.
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.
Well, it could also lead to a secret meeting between them. Luke's call might prompt Vader to arrange a discreet encounter where they can talk more freely. During this meeting, Luke could try to persuade Vader to turn back to the light side, and Vader might be more receptive than expected because of that initial call. He might share some of his inner turmoil and regrets with Luke.
The relationship could develop in a complex way. Since Vader has captured Luke, there's a power imbalance. However, as they interact, Luke might try to reach out to the good in Vader. Vader, in turn, might be conflicted. He could start to protect Luke from the Emperor's harsher plans, leading to a strange alliance within the captivity.
One reason could be that Vader represents the dark side which has brought so much destruction in the galaxy. Luke, being on the side of the Jedi and good, would naturally despise the evil deeds associated with Vader.
Often through his internal thoughts. The fanfiction might describe Luke seething with anger whenever he thinks of Vader. For example, in some stories, when Luke is meditating, his thoughts are constantly interrupted by visions of Vader and his past actions, and he can't focus because of his hatred.
Vader's reaction to Luke was intense. He was both angry and confused. Angry that Luke opposed him, but also confused by the emotions that Luke stirred within him regarding their relationship.
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.
One great fanfic could be 'The Redemption of Vader and the Ascent of Luke'. It delves deep into the relationship between the two. It shows how Luke's unwavering belief in the good in Vader starts to chip away at Vader's dark side. It's filled with intense lightsaber battles and emotional dialogues that really capture the essence of their connection in the Star Wars universe.
Well, it could be through various means. Maybe he gets some intel or follows some clues left by Luke's actions.